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  • MySQL: Return grouped fields where the group is not empty, effeciently

    - by Ryan Badour
    In one statement I'm trying to group rows of one table by joining to another table. I want to only get grouped rows where their grouped result is not empty. Ex. Items and Categories SELECT Category.id FROM Item, Category WHERE Category.id = Item.categoryId GROUP BY Category.id HAVING COUNT(Item.id) > 0 The above query gives me the results that I want but this is slow, since it has to count all the rows grouped by Category.id. What's a more effecient way? I was trying to do a Group By LIMIT to only retrieve one row per group. But my attempts failed horribly. Any idea how I can do this? Thanks

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  • MySQL: Return grouped fields where the group is not empty, efficiently

    - by Ryan Badour
    In one statement I'm trying to group rows of one table by joining to another table. I want to only get grouped rows where their grouped result is not empty. Ex. Items and Categories SELECT Category.id FROM Item, Category WHERE Category.id = Item.categoryId GROUP BY Category.id HAVING COUNT(Item.id) > 0 The above query gives me the results that I want but this is slow, since it has to count all the rows grouped by Category.id. What's a more effecient way? I was trying to do a Group By LIMIT to only retrieve one row per group. But my attempts failed horribly. Any idea how I can do this? Thanks

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  • Refresh UltraGrid's GroupBy Sort on child bands when ListChanged?

    - by Idriss
    I am using Infragistics 2009 vol 1. My UltraGrid is bound to a BindingList of business objects "A" having themself a BindingList property of business objects "B". It results in having two bands: one named "BindingList`1", the other one "ListOfB" thanks to the currency manager. I would like to refresh the GroupBy sort of the grid whenever a change is performed on the child band through the child business object and INotifyPropertyChange. If I group by a property in the child band which is a boolean (let's say "Active") and I subscribe to the event ListChanged on the bindinglist datasource with this event handler: void Grid_ListChanged(object sender, ListChangedEventArgs e) { if (e.ListChangedType == ListChangedType.ItemChanged) { string columnKey = e.PropertyDescriptor.Name; if (e.PropertyDescriptor.PropertyType.Name == "BindingList`1") { ultraGrid.DisplayLayout.Bands[columnKey].SortedColumns.RefreshSort(true); } else { UltraGridBand band = ultraGrid.DisplayLayout.Bands[0]; UltraGridColumn gc = band.Columns[columnKey]; if (gc.IsGroupByColumn || gc.SortIndicator != SortIndicator.None) { band.SortedColumns.RefreshSort(true); } ColumnFilter cf = band.ColumnFilters[columnKey]; if (cf.FilterConditions.Count > 0) { ultraGrid.DisplayLayout.RefreshFilters(); } } } } the band.SortedColumns.RefreshSort(true) is called but It gives unpredictable results in the groupby area when the property Active is changed in the child band: if one object out of three actives becomes inactive it goes from: Active : True (3 items) To: Active : False (3 items) Instead of (which is the case when I drag the column back and forth to the group by area) Active : False (1 item) Active : True (2 items) Am I doing something wrong? Is there a way to restore the expanded state of the rows when performing a RefreshSort(true); ?

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  • Linq GroupBy - how to specify the grouping key at runtime?

    - by toasteroven
    is there a good way to do a Linq GroupBy where the grouping key is determined at runtime? e.g. I want the grouping key to be built from a user-selected list of fields - can you do this? I know I can do it easily if I convert everything to a table of strings, but I was wondering if there was an elegant or clever way to accomplish this otherwise. class Item { public int A, B; public DateTime D; public double X, Y, Z; } I have a List<Item> called data. I want to do things like retrieve the sum of X grouped by A, or the sums of X, Y, and Z, grouped by A and B. but what fields go into the grouping should be able to be specified at runtime in some way.

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  • How to write this Linq SQL as a Dynamic Query (using strings)?

    - by Dr. Zim
    Skip to the "specific question" as needed. Some background: The scenario: I have a set of products with a "drill down" filter (Query Object) populated with DDLs. Each progressive DDL selection will further limit the product list as well as what options are left for the DDLs. For example, selecting a hammer out of tools limits the Product Sizes to only show hammer sizes. Current setup: I created a query object, sent it to a repository, and fed each option to a SQL "table valued function" where null values represent "get all products". I consider this a good effort, but far from DDD acceptable. I want to avoid any "programming" in SQL, hopefully doing everything with a repository. Comments on this topic would be appreciated. Specific question: How would I rewrite this query as a Dynamic Query? A link to something like 101 Linq Examples would be fantastic, but with a Dynamic Query scope. I really want to pass to this method the field in quotes "" for which I want a list of options and how many products have that option. from p in db.Products group p by p.ProductSize into g select new Category { PropertyType = g.Key, Count = g.Count() } Each DDL option will have "The selection (21)" where the (21) is the quantity of products that have that attribute. Upon selecting an option, all other remaining DDLs will update with the remaining options and counts. Edit: Additional notes: .OrderBy("it.City") // "it" refers to the entire record .GroupBy("City", "new(City)") // This produces a unique list of City .Select("it.Count()") //This gives a list of counts... getting closer .Select("key") // Selects a list of unique City .Select("new (key, count() as string)") // +1 to me LOL. key is a row of group .GroupBy("new (City, Manufacturer)", "City") // New = list of fields to group by .GroupBy("City", "new (Manufacturer, Size)") // Second parameter is a projection Product .Where("ProductType == @0", "Maps") .GroupBy("new(City)", "new ( null as string)")// Projection not available later? .Select("new (key.City, it.count() as string)")// GroupBy new makes key an object Product .Where("ProductType == @0", "Maps") .GroupBy("new(City)", "new ( null as string)")// Projection not available later? .Select("new (key.City, it as object)")// the it object is the result of GroupBy var a = Product .Where("ProductType == @0", "Maps") .GroupBy("@0", "it", "City") // This fails to group Product at all .Select("new ( Key, it as Product )"); // "it" is property cast though What I have learned so far is LinqPad is fantastic, but still looking for an answer. Eventually, completely random research like this will prevail I guess. LOL. Edit:

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  • MapReduce in DryadLINQ and PLINQ

    - by JoshReuben
    MapReduce See http://en.wikipedia.org/wiki/Mapreduce The MapReduce pattern aims to handle large-scale computations across a cluster of servers, often involving massive amounts of data. "The computation takes a set of input key/value pairs, and produces a set of output key/value pairs. The developer expresses the computation as two Func delegates: Map and Reduce. Map - takes a single input pair and produces a set of intermediate key/value pairs. The MapReduce function groups results by key and passes them to the Reduce function. Reduce - accepts an intermediate key I and a set of values for that key. It merges together these values to form a possibly smaller set of values. Typically just zero or one output value is produced per Reduce invocation. The intermediate values are supplied to the user's Reduce function via an iterator." the canonical MapReduce example: counting word frequency in a text file.     MapReduce using DryadLINQ see http://research.microsoft.com/en-us/projects/dryadlinq/ and http://connect.microsoft.com/Dryad DryadLINQ provides a simple and straightforward way to implement MapReduce operations. This The implementation has two primary components: A Pair structure, which serves as a data container. A MapReduce method, which counts word frequency and returns the top five words. The Pair Structure - Pair has two properties: Word is a string that holds a word or key. Count is an int that holds the word count. The structure also overrides ToString to simplify printing the results. The following example shows the Pair implementation. public struct Pair { private string word; private int count; public Pair(string w, int c) { word = w; count = c; } public int Count { get { return count; } } public string Word { get { return word; } } public override string ToString() { return word + ":" + count.ToString(); } } The MapReduce function  that gets the results. the input data could be partitioned and distributed across the cluster. 1. Creates a DryadTable<LineRecord> object, inputTable, to represent the lines of input text. For partitioned data, use GetPartitionedTable<T> instead of GetTable<T> and pass the method a metadata file. 2. Applies the SelectMany operator to inputTable to transform the collection of lines into collection of words. The String.Split method converts the line into a collection of words. SelectMany concatenates the collections created by Split into a single IQueryable<string> collection named words, which represents all the words in the file. 3. Performs the Map part of the operation by applying GroupBy to the words object. The GroupBy operation groups elements with the same key, which is defined by the selector delegate. This creates a higher order collection, whose elements are groups. In this case, the delegate is an identity function, so the key is the word itself and the operation creates a groups collection that consists of groups of identical words. 4. Performs the Reduce part of the operation by applying Select to groups. This operation reduces the groups of words from Step 3 to an IQueryable<Pair> collection named counts that represents the unique words in the file and how many instances there are of each word. Each key value in groups represents a unique word, so Select creates one Pair object for each unique word. IGrouping.Count returns the number of items in the group, so each Pair object's Count member is set to the number of instances of the word. 5. Applies OrderByDescending to counts. This operation sorts the input collection in descending order of frequency and creates an ordered collection named ordered. 6. Applies Take to ordered to create an IQueryable<Pair> collection named top, which contains the 100 most common words in the input file, and their frequency. Test then uses the Pair object's ToString implementation to print the top one hundred words, and their frequency.   public static IQueryable<Pair> MapReduce( string directory, string fileName, int k) { DryadDataContext ddc = new DryadDataContext("file://" + directory); DryadTable<LineRecord> inputTable = ddc.GetTable<LineRecord>(fileName); IQueryable<string> words = inputTable.SelectMany(x => x.line.Split(' ')); IQueryable<IGrouping<string, string>> groups = words.GroupBy(x => x); IQueryable<Pair> counts = groups.Select(x => new Pair(x.Key, x.Count())); IQueryable<Pair> ordered = counts.OrderByDescending(x => x.Count); IQueryable<Pair> top = ordered.Take(k);   return top; }   To Test: IQueryable<Pair> results = MapReduce(@"c:\DryadData\input", "TestFile.txt", 100); foreach (Pair words in results) Debug.Print(words.ToString());   Note: DryadLINQ applications can use a more compact way to represent the query: return inputTable         .SelectMany(x => x.line.Split(' '))         .GroupBy(x => x)         .Select(x => new Pair(x.Key, x.Count()))         .OrderByDescending(x => x.Count)         .Take(k);     MapReduce using PLINQ The pattern is relevant even for a single multi-core machine, however. We can write our own PLINQ MapReduce in a few lines. the Map function takes a single input value and returns a set of mapped values àLINQ's SelectMany operator. These are then grouped according to an intermediate key à LINQ GroupBy operator. The Reduce function takes each intermediate key and a set of values for that key, and produces any number of outputs per key à LINQ SelectMany again. We can put all of this together to implement MapReduce in PLINQ that returns a ParallelQuery<T> public static ParallelQuery<TResult> MapReduce<TSource, TMapped, TKey, TResult>( this ParallelQuery<TSource> source, Func<TSource, IEnumerable<TMapped>> map, Func<TMapped, TKey> keySelector, Func<IGrouping<TKey, TMapped>, IEnumerable<TResult>> reduce) { return source .SelectMany(map) .GroupBy(keySelector) .SelectMany(reduce); } the map function takes in an input document and outputs all of the words in that document. The grouping phase groups all of the identical words together, such that the reduce phase can then count the words in each group and output a word/count pair for each grouping: var files = Directory.EnumerateFiles(dirPath, "*.txt").AsParallel(); var counts = files.MapReduce( path => File.ReadLines(path).SelectMany(line => line.Split(delimiters)), word => word, group => new[] { new KeyValuePair<string, int>(group.Key, group.Count()) });

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  • 'Invalid column name [ColumnName]' on a nested linq query.

    - by Joe
    I've got the following query: ATable .GroupBy(x=> new {FieldA = x.FieldAID, FieldB = x.FieldBID, FieldC = x.FieldCID}) .Select(x=>new {FieldA = x.Key.FieldA, ..., last_seen = x.OrderByDescending(y=>y.Timestamp).FirstOrDefault().Timestamp}) results in: SqlException: Invalid column name 'FieldAID' x 5 SqlException: Invalid column name 'FieldBID' x 5 SqlException: Invalid column name 'FieldCID' x 1 I've worked out it has to do with the last query to Timestamp because this works: ATable .GroupBy(x=> new {FieldA = x.FieldAID, FieldB = x.FieldBID, FieldC = x.FieldCID}) .Select(x=>new {FieldA = x.Key.FieldA, ..., last_seen = x.OrderByDescending(y=>y.Timestamp).FirstOrDefault()}) The query has been simplified. The purpose is to group by a set of variables and then show the last time this grouping occured in the db. I'm using Linqpad 4 to generate these results so the Timestamp gives me a string whereas FirstOrDefault gives me the whole object which isn't ideal. Update On further testing I've noticed that the number and type of SQLException is related to the class created in the groupby clause. So, ATable .GroupBy(x=> new {FieldA = x.FieldAID}) .Select(x=>new {FieldA = x.Key.FieldA, last_seen = x.OrderByDescending(y=>y.Timestamp).FirstOrDefault()}) results in SqlException: Invalid column name 'FieldAID' x 5

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  • How to write Sql or LinqToSql for this scenario?

    - by Mike108
    How to write Sql or LinqToSql for this scenario? A table has the following data: Id UserName Price Date Status 1 Mike 2 2010-4-25 0:00:00 Success 2 Mike 3 2010-4-25 0:00:00 Fail 3 Mike 2 2010-4-25 0:00:00 Success 4 Lily 5 2010-4-25 0:00:00 Success 5 Mike 1 2010-4-25 0:00:00 Fail 6 Lily 5 2010-4-25 0:00:00 Success 7 Mike 2 2010-4-26 0:00:00 Success 8 Lily 5 2010-4-26 0:00:00 Fail 9 Lily 2 2010-4-26 0:00:00 Success 10 Lily 1 2010-4-26 0:00:00 Fail I want to get the summary result from the data, the result should be: UserName Date TotalPrice TotalRecord SuccessRecord FailRecord Mike 2010-04-25 8 4 2 2 Lily 2010-04-25 10 2 2 0 Mike 2010-04-26 2 1 1 0 Lily 2010-04-26 8 3 1 2 The TotalPrice is the sum(Price) groupby UserName and Date The TotalRecord is the count(*) groupby UserName and Date The SuccessRecord is the count(*) groupby UserName and Date where Status='Success' The FailRecord is the count(*) groupby UserName and Date where Status='Fail' The TotalRecord = SuccessRecord + FailRecord The sql server 2005 database script is: /****** Object: Table [dbo].[Pay] Script Date: 04/28/2010 22:23:42 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO IF NOT EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[Pay]') AND type in (N'U')) BEGIN CREATE TABLE [dbo].[Pay]( [Id] [int] IDENTITY(1,1) NOT NULL, [UserName] [nvarchar](50) COLLATE Chinese_PRC_CI_AS NULL, [Price] [int] NULL, [Date] [datetime] NULL, [Status] [nvarchar](50) COLLATE Chinese_PRC_CI_AS NULL, CONSTRAINT [PK_Pay] PRIMARY KEY CLUSTERED ( [Id] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ) END GO SET IDENTITY_INSERT [dbo].[Pay] ON INSERT [dbo].[Pay] ([Id], [UserName], [Price], [Date], [Status]) VALUES (1, N'Mike', 2, CAST(0x00009D6300000000 AS DateTime), N'Success') INSERT [dbo].[Pay] ([Id], [UserName], [Price], [Date], [Status]) VALUES (2, N'Mike', 3, CAST(0x00009D6300000000 AS DateTime), N'Fail') INSERT [dbo].[Pay] ([Id], [UserName], [Price], [Date], [Status]) VALUES (3, N'Mike', 2, CAST(0x00009D6300000000 AS DateTime), N'Success') INSERT [dbo].[Pay] ([Id], [UserName], [Price], [Date], [Status]) VALUES (4, N'Lily', 5, CAST(0x00009D6300000000 AS DateTime), N'Success') INSERT [dbo].[Pay] ([Id], [UserName], [Price], [Date], [Status]) VALUES (5, N'Mike', 1, CAST(0x00009D6300000000 AS DateTime), N'Fail') INSERT [dbo].[Pay] ([Id], [UserName], [Price], [Date], [Status]) VALUES (6, N'Lily', 5, CAST(0x00009D6300000000 AS DateTime), N'Success') INSERT [dbo].[Pay] ([Id], [UserName], [Price], [Date], [Status]) VALUES (7, N'Mike', 2, CAST(0x00009D6400000000 AS DateTime), N'Success') INSERT [dbo].[Pay] ([Id], [UserName], [Price], [Date], [Status]) VALUES (8, N'Lily', 5, CAST(0x00009D6400000000 AS DateTime), N'Fail') INSERT [dbo].[Pay] ([Id], [UserName], [Price], [Date], [Status]) VALUES (9, N'Lily', 2, CAST(0x00009D6400000000 AS DateTime), N'Success') INSERT [dbo].[Pay] ([Id], [UserName], [Price], [Date], [Status]) VALUES (10, N'Lily', 1, CAST(0x00009D6400000000 AS DateTime), N'Fail') SET IDENTITY_INSERT [dbo].[Pay] OFF

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  • How do I strip multiple (optional) parts of a SQL string using .NET Regular Expressions?

    - by Luc
    I've been working on this for a few hours now and can't find any help on it. Basically, I'm trying to strip a SQL string into various parts (fields, from, where, having, groupBy, orderBy). I refuse to believe that I'm the first person to ever try to do this, so I'd like to ask for some advise from the StackOverflow community. :) To understand what I need, assume the following SQL string: select * from table1 inner join table2 on table1.id = table2.id where field1 = 'sam' having table1.field3 > 0 group by table1.field4 order by table1.field5 I created a regular expression to group the parts accordingly: select\s+(?<fields>.+)\s+from\s+(?<from>.+)\s+where\s+(?<where>.+)\s+having\s+(?<having>.+)\s+group\sby\s+(?<groupby>.+)\s+order\sby\s+(?<orderby>.+) This gives me the following results: fields => * from => table1 inner join table2 on table1.id = table2.id where => field1 = 'sam' having => table1.field3 > 0 groupby => table1.field4 orderby => table1.field5 The problem that I'm faced with is that if any part of the SQL string is missing after the 'from' clause, the regular expression doesn't match. To fix that, I've tried putting each optional part in it's own (...)? group but that doesn't work. It simply put all the optional parts (where, having, groupBy, and orderBy) into the 'from' group. Any ideas?

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  • Best ways to format LINQ queries.

    - by Aren B
    Before you ignore / vote-to-close this question, I consider this a valid question to ask because code clarity is an important topic of discussion, it's essential to writing maintainable code and I would greatly appreciate answers from those who have come across this before. I've recently run into this problem, LINQ queries can get pretty nasty real quick because of the large amount of nesting. Below are some examples of the differences in formatting that I've come up with (for the same relatively non-complex query) No Formatting var allInventory = system.InventorySources.Select(src => new { Inventory = src.Value.GetInventory(product.OriginalProductId, true), Region = src.Value.Region }).GroupBy(i => i.Region, i => i.Inventory); Elevated Formatting var allInventory = system.InventorySources .Select(src => new { Inventory = src.Value.GetInventory(product.OriginalProductId, true), Region = src.Value.Region }) .GroupBy( i => i.Region, i => i.Inventory); Block Formatting var allInventory = system.InventorySources .Select( src => new { Inventory = src.Value.GetInventory(product.OriginalProductId, true), Region = src.Value.Region }) .GroupBy( i => i.Region, i => i.Inventory ); List Formatting var allInventory = system.InventorySources .Select(src => new { Inventory = src.Value.GetInventory(product.OriginalProductId, true), Region = src.Value.Region }) .GroupBy(i => i.Region, i => i.Inventory); I want to come up with a standard for linq formatting so that it maximizes readability & understanding and looks clean and professional. So far I can't decide so I turn the question to the professionals here.

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  • How to find subgroups statistics in pandas?

    - by user2808117
    I am grouping a DataFrame using multiple columns (e.g., columns A, B - my_df.groupby(['A','B']) ), is there a better (less lines of code, faster) way of finding how many rows are in each subgroup and how many subgroups are there in total? at the moment I am using: def get_grp_size(grp): grp['size'] = len(grp) return grp my_df = my_df.groupby(['A','B']).apply(get_grp_size) my_df[['A','B','size']].drop_duplicates().size

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  • Changes to the LINQ-to-StreamInsight Dialect

    - by Roman Schindlauer
    In previous versions of StreamInsight (1.0 through 2.0), CepStream<> represents temporal streams of many varieties: Streams with ‘open’ inputs (e.g., those defined and composed over CepStream<T>.Create(string streamName) Streams with ‘partially bound’ inputs (e.g., those defined and composed over CepStream<T>.Create(Type adapterFactory, …)) Streams with fully bound inputs (e.g., those defined and composed over To*Stream – sequences or DQC) The stream may be embedded (where Server.Create is used) The stream may be remote (where Server.Connect is used) When adding support for new programming primitives in StreamInsight 2.1, we faced a choice: Add a fourth variety (use CepStream<> to represent streams that are bound the new programming model constructs), or introduce a separate type that represents temporal streams in the new user model. We opted for the latter. Introducing a new type has the effect of reducing the number of (confusing) runtime failures due to inappropriate uses of CepStream<> instances in the incorrect context. The new types are: IStreamable<>, which logically represents a temporal stream. IQStreamable<> : IStreamable<>, which represents a queryable temporal stream. Its relationship to IStreamable<> is analogous to the relationship of IQueryable<> to IEnumerable<>. The developer can compose temporal queries over remote stream sources using this type. The syntax of temporal queries composed over IQStreamable<> is mostly consistent with the syntax of our existing CepStream<>-based LINQ provider. However, we have taken the opportunity to refine certain aspects of the language surface. Differences are outlined below. Because 2.1 introduces new types to represent temporal queries, the changes outlined in this post do no impact existing StreamInsight applications using the existing types! SelectMany StreamInsight does not support the SelectMany operator in its usual form (which is analogous to SQL’s “CROSS APPLY” operator): static IEnumerable<R> SelectMany<T, R>(this IEnumerable<T> source, Func<T, IEnumerable<R>> collectionSelector) It instead uses SelectMany as a convenient syntactic representation of an inner join. The parameter to the selector function is thus unavailable. Because the parameter isn’t supported, its type in StreamInsight 1.0 – 2.0 wasn’t carefully scrutinized. Unfortunately, the type chosen for the parameter is nonsensical to LINQ programmers: static CepStream<R> SelectMany<T, R>(this CepStream<T> source, Expression<Func<CepStream<T>, CepStream<R>>> streamSelector) Using Unit as the type for the parameter accurately reflects the StreamInsight’s capabilities: static IQStreamable<R> SelectMany<T, R>(this IQStreamable<T> source, Expression<Func<Unit, IQStreamable<R>>> streamSelector) For queries that succeed – that is, queries that do not reference the stream selector parameter – there is no difference between the code written for the two overloads: from x in xs from y in ys select f(x, y) Top-K The Take operator used in StreamInsight causes confusion for LINQ programmers because it is applied to the (unbounded) stream rather than the (bounded) window, suggesting that the query as a whole will return k rows: (from win in xs.SnapshotWindow() from x in win orderby x.A select x.B).Take(k) The use of SelectMany is also unfortunate in this context because it implies the availability of the window parameter within the remainder of the comprehension. The following compiles but fails at runtime: (from win in xs.SnapshotWindow() from x in win orderby x.A select win).Take(k) The Take operator in 2.1 is applied to the window rather than the stream: Before After (from win in xs.SnapshotWindow() from x in win orderby x.A select x.B).Take(k) from win in xs.SnapshotWindow() from b in     (from x in win     orderby x.A     select x.B).Take(k) select b Multicast We are introducing an explicit multicast operator in order to preserve expression identity, which is important given the semantics about moving code to and from StreamInsight. This also better matches existing LINQ dialects, such as Reactive. This pattern enables expressing multicasting in two ways: Implicit Explicit var ys = from x in xs          where x.A > 1          select x; var zs = from y1 in ys          from y2 in ys.ShiftEventTime(_ => TimeSpan.FromSeconds(1))          select y1 + y2; var ys = from x in xs          where x.A > 1          select x; var zs = ys.Multicast(ys1 =>     from y1 in ys1     from y2 in ys1.ShiftEventTime(_ => TimeSpan.FromSeconds(1))     select y1 + y2; Notice the product translates an expression using implicit multicast into an expression using the explicit multicast operator. The user does not see this translation. Default window policies Only default window policies are supported in the new surface. Other policies can be simulated by using AlterEventLifetime. Before After xs.SnapshotWindow(     WindowInputPolicy.ClipToWindow,     SnapshotWindowInputPolicy.Clip) xs.SnapshotWindow() xs.TumblingWindow(     TimeSpan.FromSeconds(1),     HoppingWindowOutputPolicy.PointAlignToWindowEnd) xs.TumblingWindow(     TimeSpan.FromSeconds(1)) xs.TumblingWindow(     TimeSpan.FromSeconds(1),     HoppingWindowOutputPolicy.ClipToWindowEnd) Not supported … LeftAntiJoin Representation of LASJ as a correlated sub-query in the LINQ surface is problematic as the StreamInsight engine does not support correlated sub-queries (see discussion of SelectMany). The current syntax requires the introduction of an otherwise unsupported ‘IsEmpty()’ operator. As a result, the pattern is not discoverable and implies capabilities not present in the server. The direct representation of LASJ is used instead: Before After from x in xs where     (from y in ys     where x.A > y.B     select y).IsEmpty() select x xs.LeftAntiJoin(ys, (x, y) => x.A > y.B) from x in xs where     (from y in ys     where x.A == y.B     select y).IsEmpty() select x xs.LeftAntiJoin(ys, x => x.A, y => y.B) ApplyWithUnion The ApplyWithUnion methods have been deprecated since their signatures are redundant given the standard SelectMany overloads: Before After xs.GroupBy(x => x.A).ApplyWithUnion(gs => from win in gs.SnapshotWindow() select win.Count()) xs.GroupBy(x => x.A).SelectMany(     gs =>     from win in gs.SnapshotWindow()     select win.Count()) xs.GroupBy(x => x.A).ApplyWithUnion(gs => from win in gs.SnapshotWindow() select win.Count(), r => new { r.Key, Count = r.Payload }) from x in xs group x by x.A into gs from win in gs.SnapshotWindow() select new { gs.Key, Count = win.Count() } Alternate UDO syntax The representation of UDOs in the StreamInsight LINQ dialect confuses cardinalities. Based on the semantics of user-defined operators in StreamInsight, one would expect to construct queries in the following form: from win in xs.SnapshotWindow() from y in MyUdo(win) select y Instead, the UDO proxy method is referenced within a projection, and the (many) results returned by the user code are automatically flattened into a stream: from win in xs.SnapshotWindow() select MyUdo(win) The “many-or-one” confusion is exemplified by the following example that compiles but fails at runtime: from win in xs.SnapshotWindow() select MyUdo(win) + win.Count() The above query must fail because the UDO is in fact returning many values per window while the count aggregate is returning one. Original syntax New alternate syntax from win in xs.SnapshotWindow() select win.UdoProxy(1) from win in xs.SnapshotWindow() from y in win.UserDefinedOperator(() => new Udo(1)) select y -or- from win in xs.SnapshotWindow() from y in win.UdoMacro(1) select y Notice that this formulation also sidesteps the dynamic type pitfalls of the existing “proxy method” approach to UDOs, in which the type of the UDO implementation (TInput, TOuput) and the type of its constructor arguments (TConfig) need to align in a precise and non-obvious way with the argument and return types for the corresponding proxy method. UDSO syntax UDSO currently leverages the DataContractSerializer to clone initial state for logical instances of the user operator. Initial state will instead be described by an expression in the new LINQ surface. Before After xs.Scan(new Udso()) xs.Scan(() => new Udso()) Name changes ShiftEventTime => AlterEventStartTime: The alter event lifetime overload taking a new start time value has been renamed. CountByStartTimeWindow => CountWindow

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  • Changes to the LINQ-to-StreamInsight Dialect

    - by Roman Schindlauer
    In previous versions of StreamInsight (1.0 through 2.0), CepStream<> represents temporal streams of many varieties: Streams with ‘open’ inputs (e.g., those defined and composed over CepStream<T>.Create(string streamName) Streams with ‘partially bound’ inputs (e.g., those defined and composed over CepStream<T>.Create(Type adapterFactory, …)) Streams with fully bound inputs (e.g., those defined and composed over To*Stream – sequences or DQC) The stream may be embedded (where Server.Create is used) The stream may be remote (where Server.Connect is used) When adding support for new programming primitives in StreamInsight 2.1, we faced a choice: Add a fourth variety (use CepStream<> to represent streams that are bound the new programming model constructs), or introduce a separate type that represents temporal streams in the new user model. We opted for the latter. Introducing a new type has the effect of reducing the number of (confusing) runtime failures due to inappropriate uses of CepStream<> instances in the incorrect context. The new types are: IStreamable<>, which logically represents a temporal stream. IQStreamable<> : IStreamable<>, which represents a queryable temporal stream. Its relationship to IStreamable<> is analogous to the relationship of IQueryable<> to IEnumerable<>. The developer can compose temporal queries over remote stream sources using this type. The syntax of temporal queries composed over IQStreamable<> is mostly consistent with the syntax of our existing CepStream<>-based LINQ provider. However, we have taken the opportunity to refine certain aspects of the language surface. Differences are outlined below. Because 2.1 introduces new types to represent temporal queries, the changes outlined in this post do no impact existing StreamInsight applications using the existing types! SelectMany StreamInsight does not support the SelectMany operator in its usual form (which is analogous to SQL’s “CROSS APPLY” operator): static IEnumerable<R> SelectMany<T, R>(this IEnumerable<T> source, Func<T, IEnumerable<R>> collectionSelector) It instead uses SelectMany as a convenient syntactic representation of an inner join. The parameter to the selector function is thus unavailable. Because the parameter isn’t supported, its type in StreamInsight 1.0 – 2.0 wasn’t carefully scrutinized. Unfortunately, the type chosen for the parameter is nonsensical to LINQ programmers: static CepStream<R> SelectMany<T, R>(this CepStream<T> source, Expression<Func<CepStream<T>, CepStream<R>>> streamSelector) Using Unit as the type for the parameter accurately reflects the StreamInsight’s capabilities: static IQStreamable<R> SelectMany<T, R>(this IQStreamable<T> source, Expression<Func<Unit, IQStreamable<R>>> streamSelector) For queries that succeed – that is, queries that do not reference the stream selector parameter – there is no difference between the code written for the two overloads: from x in xs from y in ys select f(x, y) Top-K The Take operator used in StreamInsight causes confusion for LINQ programmers because it is applied to the (unbounded) stream rather than the (bounded) window, suggesting that the query as a whole will return k rows: (from win in xs.SnapshotWindow() from x in win orderby x.A select x.B).Take(k) The use of SelectMany is also unfortunate in this context because it implies the availability of the window parameter within the remainder of the comprehension. The following compiles but fails at runtime: (from win in xs.SnapshotWindow() from x in win orderby x.A select win).Take(k) The Take operator in 2.1 is applied to the window rather than the stream: Before After (from win in xs.SnapshotWindow() from x in win orderby x.A select x.B).Take(k) from win in xs.SnapshotWindow() from b in     (from x in win     orderby x.A     select x.B).Take(k) select b Multicast We are introducing an explicit multicast operator in order to preserve expression identity, which is important given the semantics about moving code to and from StreamInsight. This also better matches existing LINQ dialects, such as Reactive. This pattern enables expressing multicasting in two ways: Implicit Explicit var ys = from x in xs          where x.A > 1          select x; var zs = from y1 in ys          from y2 in ys.ShiftEventTime(_ => TimeSpan.FromSeconds(1))          select y1 + y2; var ys = from x in xs          where x.A > 1          select x; var zs = ys.Multicast(ys1 =>     from y1 in ys1     from y2 in ys1.ShiftEventTime(_ => TimeSpan.FromSeconds(1))     select y1 + y2; Notice the product translates an expression using implicit multicast into an expression using the explicit multicast operator. The user does not see this translation. Default window policies Only default window policies are supported in the new surface. Other policies can be simulated by using AlterEventLifetime. Before After xs.SnapshotWindow(     WindowInputPolicy.ClipToWindow,     SnapshotWindowInputPolicy.Clip) xs.SnapshotWindow() xs.TumblingWindow(     TimeSpan.FromSeconds(1),     HoppingWindowOutputPolicy.PointAlignToWindowEnd) xs.TumblingWindow(     TimeSpan.FromSeconds(1)) xs.TumblingWindow(     TimeSpan.FromSeconds(1),     HoppingWindowOutputPolicy.ClipToWindowEnd) Not supported … LeftAntiJoin Representation of LASJ as a correlated sub-query in the LINQ surface is problematic as the StreamInsight engine does not support correlated sub-queries (see discussion of SelectMany). The current syntax requires the introduction of an otherwise unsupported ‘IsEmpty()’ operator. As a result, the pattern is not discoverable and implies capabilities not present in the server. The direct representation of LASJ is used instead: Before After from x in xs where     (from y in ys     where x.A > y.B     select y).IsEmpty() select x xs.LeftAntiJoin(ys, (x, y) => x.A > y.B) from x in xs where     (from y in ys     where x.A == y.B     select y).IsEmpty() select x xs.LeftAntiJoin(ys, x => x.A, y => y.B) ApplyWithUnion The ApplyWithUnion methods have been deprecated since their signatures are redundant given the standard SelectMany overloads: Before After xs.GroupBy(x => x.A).ApplyWithUnion(gs => from win in gs.SnapshotWindow() select win.Count()) xs.GroupBy(x => x.A).SelectMany(     gs =>     from win in gs.SnapshotWindow()     select win.Count()) xs.GroupBy(x => x.A).ApplyWithUnion(gs => from win in gs.SnapshotWindow() select win.Count(), r => new { r.Key, Count = r.Payload }) from x in xs group x by x.A into gs from win in gs.SnapshotWindow() select new { gs.Key, Count = win.Count() } Alternate UDO syntax The representation of UDOs in the StreamInsight LINQ dialect confuses cardinalities. Based on the semantics of user-defined operators in StreamInsight, one would expect to construct queries in the following form: from win in xs.SnapshotWindow() from y in MyUdo(win) select y Instead, the UDO proxy method is referenced within a projection, and the (many) results returned by the user code are automatically flattened into a stream: from win in xs.SnapshotWindow() select MyUdo(win) The “many-or-one” confusion is exemplified by the following example that compiles but fails at runtime: from win in xs.SnapshotWindow() select MyUdo(win) + win.Count() The above query must fail because the UDO is in fact returning many values per window while the count aggregate is returning one. Original syntax New alternate syntax from win in xs.SnapshotWindow() select win.UdoProxy(1) from win in xs.SnapshotWindow() from y in win.UserDefinedOperator(() => new Udo(1)) select y -or- from win in xs.SnapshotWindow() from y in win.UdoMacro(1) select y Notice that this formulation also sidesteps the dynamic type pitfalls of the existing “proxy method” approach to UDOs, in which the type of the UDO implementation (TInput, TOuput) and the type of its constructor arguments (TConfig) need to align in a precise and non-obvious way with the argument and return types for the corresponding proxy method. UDSO syntax UDSO currently leverages the DataContractSerializer to clone initial state for logical instances of the user operator. Initial state will instead be described by an expression in the new LINQ surface. Before After xs.Scan(new Udso()) xs.Scan(() => new Udso()) Name changes ShiftEventTime => AlterEventStartTime: The alter event lifetime overload taking a new start time value has been renamed. CountByStartTimeWindow => CountWindow

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  • PHP PSR-0 + several namespaces in one file and autoload

    - by Nemoden
    I've been thinking for a while about defining several namespaces in one php file and so, having several classes inside this file. Suppose, I want to implement something like Doctrine\ORM\Query\Expr: Expr.php Expr |-- Andx.php |-- Base.php |-- Comparison.php |-- Composite.php |-- From.php |-- Func.php |-- GroupBy.php |-- Join.php |-- Literal.php |-- Math.php |-- OrderBy.php |-- Orx.php `-- Select.php It would be nice if I had all of this in one file - Expr.php: namespace Doctrine\ORM\Query; class Expr { // code } namespace Doctrine\ORM\Query\Expr; class Func { // code } // etc... What I'm thinking of is directories naming convention and, unlike PSR-0 having several classes and namespaces in one file. It's best explained by the code: ls Doctrine/orm/query Expr.php that's it - only Expr.php Since Expr.php is somewhat I call a "meta-namespace" for Expr\Func, it make sense to place all the classes inside Expr.php (as shown above). So, the vendor name is still starts with an uppercased letter (Doctrine) and the other parts of namespace start with lowercased letter. We can write an autoload so it would respect this notion: function load_class($class) { if (class_exists($class)) { return true; } $tokenized_path = explode(array("_", "\\"), DIRECTORY_SEPARATOR, $class); // array('Doctrine', 'orm', 'query', 'Expr', 'Func'); // ^^^^ // first, we are looking for first uppercased namespace part // and if it's not last (not the class name), we use it as a filename // and wiping away the rest to compose a path to a file we need to include if (FALSE !== ($meta_class_index = find_meta_class($tokenized_path))) { $new_tokenized_path = array_slice($tokenized_path, 0, $meta_class_index); $path_to_class = implode(DIRECTORY_SEPARATOR, $new_tokenized_path); } else { // no meta class found $path_to_class = implode(DIRECTORY_SEPARATOR, $tokenized_path); } if (file_exists($path_to_class.'.php')) { require_once $path_to_class.'.php'; } return false; } Another reason to do so is to reduce a number of php files scattered among directories. Usually you check file existence before you require a file to fail gracefully: file_exists($path_to_class.'.php'); If you take a look at actual Doctrine\ORM\Query\Expr code, you'll see they use all of the "inner-classes", so you actually do: file_exists("/path/to/Doctrine/ORM/Query/Expr.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/AndX.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/Base.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/Comparison.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/Composite.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/From.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/Func.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/GroupBy.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/Join.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/Literal.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/Math.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/OrderBy.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/Orx.php"); file_exists("/path/to/Doctrine/ORM/Query/Expr/Select.php"); in your autoload which causes quite a few I/O reads. Isn't it too much to check on each user's hit? I'm just putting this on a discussion. I want to hear from another PHP programmers what do they think of it. And, of course, if you have a silver bullet addressing this problems I've designated here, please share. I also have been thinking if my vogue question fits here and according to the FAQ it seems like this question addresses "software architecture" problem slash proposal. I'm sorry if my scribble may seem a bit clunky :) Thanks.

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  • Exclude rows with Doctrine ORM DQL (NOT IN)

    - by Sheriffen
    I'm building a chat application with codeigniter and doctrine. Tables: - User - User_roles - User_available Relations: ONE user have MANY roles. ONE user_available have ONE user. Users available for chatting will be in the user_available table. Problem: I need to get all users in in user_available that hasn't got role_id 7. So I need to express in DQL something like (this is not even SQL, just in words): SELECT * from user_available WHERE NOT user_available.User.Role.role_id = 7 Really stuck on this one EDIT: Guess I was unclear. The tables are already mapped and Doctrine does the INNER JOIN job for me. I'm using this code to get the admin that waited the longest but now I need the user: $admin = Doctrine_Query::create() ->select('c.id') ->from('Chat_available c') ->where('c.User.Roles.role_id = ?', 7) ->groupBy('c.id') ->orderBy('c.created_at ASC') ->fetchOne(); Now I need to get the user that waited the longest but this does NOT work $admin = Doctrine_Query::create() ->select('c.id') ->from('Chat_available c') ->where('c.User.Roles.role_id != ?', 7) ->groupBy('c.id') ->orderBy('c.created_at ASC') ->fetchOne();

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  • Using Linq to group a list of objects into a new grouped list of list of objects

    - by Simon G
    Hi, I don't know if this is possible in Linq but here goes... I have an object: public class User { public int UserID { get; set; } public string UserName { get; set; } public int GroupID { get; set; } } I return a list that may look like the following: List<User> userList = new List<User>(); userList.Add( new User { UserID = 1, UserName = "UserOne", GroupID = 1 } ); userList.Add( new User { UserID = 2, UserName = "UserTwo", GroupID = 1 } ); userList.Add( new User { UserID = 3, UserName = "UserThree", GroupID = 2 } ); userList.Add( new User { UserID = 4, UserName = "UserFour", GroupID = 1 } ); userList.Add( new User { UserID = 5, UserName = "UserFive", GroupID = 3 } ); userList.Add( new User { UserID = 6, UserName = "UserSix", GroupID = 3 } ); I want to be able to run a Linq query on the above list that groups all the users by GroupID. So the out pub will be a list of user lists that contains user (if that makes sense?). So the out put would be something like: GroupedUserList UserList UserID = 1, UserName = "UserOne", GroupID = 1 UserID = 2, UserName = "UserTwo", GroupID = 1 UserID = 4, UserName = "UserFour", GroupID = 1 UserList UserID = 3, UserName = "UserThree", GroupID = 2 UserList UserID = 5, UserName = "UserFive", GroupID = 3 UserID = 6, UserName = "UserSix", GroupID = 3 I've tried using the groupby linq clause but this seems to return a list of keys and its not grouped by correctly: var groupedCustomerList = userList.GroupBy( u => u.GroupID ).ToList(); Any help would be much appreciated. Thanks

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  • Distinct() to return List<> returning Duplicates

    - by KDM
    I have a list of Filters that are passed into a webservice and I iterate over the collection and do Linq query and then add to the list of products but when I do a GroupBy and Distinct() it doesn't remove the duplicates. I am using a IEnumerable because when you use Disinct it converts it to IEnumerable. If you know how to construct this better and make my function return a type of List<Product> that would be appreciated thanks. Here is my code in C#: if (Tab == "All-Items") { List<Product> temp = new List<Product>(); List<Product> Products2 = new List<Product>(); foreach (Filter filter in Filters) { List<Product> products = (from p in db.Products where p.Discontinued == false && p.DepartmentId == qDepartment.Id join f in db.Filters on p.Id equals f.ProductId join x in db.ProductImages on p.Id equals x.ProductId where x.Dimension == "180X180" && f.Name == filter.Name /*Filter*/ select new Product { Id = p.Id, Title = p.Title, ShortDescription = p.ShortDescription, Brand = p.Brand, Model = p.Model, Image = x.Path, FriendlyUrl = p.FriendlyUrl, SellPrice = p.SellPrice, DiscountPercentage = p.DiscountPercentage, Votes = p.Votes, TotalRating = p.TotalRating }).ToList<Product>(); foreach (Product p in products) { temp.Add(p); } IEnumerable temp2 = temp.GroupBy(x => x.Id).Distinct(); IEnumerator e = temp.GetEnumerator(); while (e.MoveNext()) { Product c = e.Current as Product; Products2.Add(c); } } pf.Products = Products2;// return type must be List<Product> }

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  • How to break an object into chunks based on some property?

    - by CurlyFro
    public class InvestorMailing { public string To { get; set; } public IEnumerable<string> Attachments { get; set; } public int AttachmentCount { get; set; } public long AttachmentSize { get; set; } } i have an IList<InvestorMailing> mailingList. if the attachment size is greater than x, then i need to split my object into chunks. is there an easy linq-y way to do this? Edited: this is how i'm generating my mailings: var groupedMailings = mailingList.GroupBy(g => g.GroupBy); var investorMailings = groupedMailings.Select( g => new DistinctInvestorMailing { Id = g.Select(x => x.Id).FirstOrDefault(), To = g.Key.Trim(), From = g.Select(x => x.From).FirstOrDefault(), FromName = g.Select(x => x.FromName).FirstOrDefault(), Bcc = g.Select(x => x.Bcc).FirstOrDefault(), DeliveryCode = g.Select(x => x.DeliveryCode).FirstOrDefault(), Subject = g.Select(x => x.Subject).FirstOrDefault(), Body = g.Select(x => x.Body).FirstOrDefault(), CommentsOnStatus = g.Select(x => x.CommentsOnStatus).FirstOrDefault(), Attachments = g.Select(x => x.AttachmentPath), AttachmentCount = g.Select(x => x.AttachmentPath).Count(), AttachmentSize = g.Sum(x => x.AttachmentSize), MailType = g.Select(x => x.MessageType).FirstOrDefault() } ).ToList();

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  • Sort wss3.0 view by more than 2 columns

    - by russellGove
    Does anyone know if it's possible to sort a sharepoint list view bymore than 3 columns. It doesn't let me do it in the UI and whwn I added this: > <Query> > <GroupBy Collapse="TRUE" GroupLimit="100"> > <FieldRef Name="Category" /> > <FieldRef Name="SubCategory" /> > <FieldRef Name="Topic" /> > </GroupBy> > <OrderBy> > <FieldRef Name="Category" /> > <FieldRef Name="SubCategory" /> > <FieldRef Name="Topic" /> > </OrderBy> > </Query> I get an error on the page: <!-- #RENDER FAILED -->

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  • Excel VBA (2007) Subtotal method of Range class failed

    - by robihot
    Hi, I'm getting a Subtotal method of Range class failed Error when i try to run a macro. Code works GREAT (no errors) when i run it using Excel 2003. Here's a snippet... 'SubTotal Sheet Range("A1").Select Selection.Subtotal GroupBy:=1, Function:=xlSum, TotalList:=Array(3, 4, 5, 6, 7, _ 8, 9), Replace:=True, PageBreaks:=False, SummaryBelowData:=True Any help would be appreciated !!!

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  • Excel VBA (2007) Subtotal method of Range class failed

    - by robihot
    I'm getting a Subtotal method of Range class failed Error when I try to run a macro in Excel 2007. Code works GREAT (no errors) when I run it using Excel 2003. Here's a snippet... 'SubTotal Sheet Range("A1").Select Selection.Subtotal GroupBy:=1, Function:=xlSum, TotalList:=Array(3, 4, 5, 6, 7, _ 8, 9), Replace:=True, PageBreaks:=False, SummaryBelowData:=True Any help would be appreciated.

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  • How to get distinct values from the List&lt;T&gt; with LINQ

    - by Vincent Maverick Durano
    Recently I was working with data from a generic List<T> and one of my objectives is to get the distinct values that is found in the List. Consider that we have this simple class that holds the following properties: public class Product { public string Make { get; set; } public string Model { get; set; } }   Now in the page code behind we will create a list of product by doing the following: private List<Product> GetProducts() { List<Product> products = new List<Product>(); Product p = new Product(); p.Make = "Samsung"; p.Model = "Galaxy S 1"; products.Add(p); p = new Product(); p.Make = "Samsung"; p.Model = "Galaxy S 2"; products.Add(p); p = new Product(); p.Make = "Samsung"; p.Model = "Galaxy Note"; products.Add(p); p = new Product(); p.Make = "Apple"; p.Model = "iPhone 4"; products.Add(p); p = new Product(); p.Make = "Apple"; p.Model = "iPhone 4s"; products.Add(p); p = new Product(); p.Make = "HTC"; p.Model = "Sensation"; products.Add(p); p = new Product(); p.Make = "HTC"; p.Model = "Desire"; products.Add(p); p = new Product(); p.Make = "Nokia"; p.Model = "Some Model"; products.Add(p); p = new Product(); p.Make = "Nokia"; p.Model = "Some Model"; products.Add(p); p = new Product(); p.Make = "Sony Ericsson"; p.Model = "800i"; products.Add(p); p = new Product(); p.Make = "Sony Ericsson"; p.Model = "800i"; products.Add(p); return products; }   And then let’s bind the products to the GridView. protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { Gridview1.DataSource = GetProducts(); Gridview1.DataBind(); } }   Running the code will display something like this in the page: Now what I want is to get the distinct row values from the list. So what I did is to use the LINQ Distinct operator and unfortunately it doesn't work. In order for it work is you must use the overload method of the Distinct operator for you to get the desired results. So I’ve added this IEqualityComparer<T> class to compare values: class ProductComparer : IEqualityComparer<Product> { public bool Equals(Product x, Product y) { if (Object.ReferenceEquals(x, y)) return true; if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null)) return false; return x.Make == y.Make && x.Model == y.Model; } public int GetHashCode(Product product) { if (Object.ReferenceEquals(product, null)) return 0; int hashProductName = product.Make == null ? 0 : product.Make.GetHashCode(); int hashProductCode = product.Model.GetHashCode(); return hashProductName ^ hashProductCode; } }   After that you can then bind the GridView like this: protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { Gridview1.DataSource = GetProducts().Distinct(new ProductComparer()); Gridview1.DataBind(); } }   Running the page will give you the desired output below: As you notice, it now eliminates the duplicate rows in the GridView. Now what if we only want to get the distinct values for a certain field. For example I want to get the distinct “Make” values such as Samsung, Apple, HTC, Nokia and Sony Ericsson and populate them to a DropDownList control for filtering purposes. I was hoping the the Distinct operator has an overload that can compare values based on the property value like (GetProducts().Distinct(o => o.PropertyToCompare). But unfortunately it doesn’t provide that overload so what I did as a workaround is to use the GroupBy,Select and First LINQ query operators to achieve what I want. Here’s the code to get the distinct values of a certain field. protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { DropDownList1.DataSource = GetProducts().GroupBy(o => o.Make).Select(o => o.First()); DropDownList1.DataTextField = "Make"; DropDownList1.DataValueField = "Model"; DropDownList1.DataBind(); } } Running the code will display the following output below:   That’s it! I hope someone find this post useful!

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  • Hex Dump using LINQ (in 7 lines of code)

    Eric White has posted an interesting LINQ query on his blog that shows how to create a Hex Dump in something like 7 lines of code.Of course, this is not production grade code, but it's another good example that demonstrates the expressiveness of LINQ.Here is the code:byte[] ba = File.ReadAllBytes("test.xml");int bytesPerLine = 16;string hexDump = ba.Select((c, i) => new { Char = c, Chunk = i / bytesPerLine })    .GroupBy(c => c.Chunk)    .Select(g => g.Select(c...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Itertools group by functionality

    - by Nil
    I want to group by on dict key >>> x [{'a': 10, 'b': 90}, {'a': 20}, {'a': 30}, {'a': 10}] >>> [(name, list(group)) for name, group in groupby(x, lambda p:p['a'])] [(10, [{'a': 10, 'b': 90}]), (20, [{'a': 20}]), (30, [{'a': 30}]), (10, [{'a': 10}])] This must group on key 10 :(

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