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  • How to make a SUM of Dictionary Value nested into a list with LINQ ?

    - by user551108
    Hi All, I have a product object declared as : Product { int ProductID; string ProductName; int ProductTypeID; string ProductTypeName; int UnitsSold Dictionary <string, int> UnitsSoldByYear; } I want to make a sum on UnitsSold and UnitsSoldByYear properties with a Linq query but I didn't know how to make this kind of sum on a dictionary ! Here is my begining linq query code : var ProductTypeSum = from i in ProductsList group i by new { i.ProductTypeID, i.ProductTypeName} into pt select new { ProductTypeID= pt.Key.ProductTypeID, ProductTypeName= pt.Key.ProductTypeName, UnitsSoldSum= pt.Sum(i => i.UnitsSold), // How to make a Dictionary sum here } Thank you for your help !

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  • LINQ to XML

    Gain an understanding of LINQ (Language Integrated Query) to XML and see why you'll never want to use the DOM again.

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  • C# Multiple Property Sort

    - by Ben Griswold
    As you can see in the snippet below, sorting is easy with Linq.  Simply provide your OrderBy criteria and you’re done.  If you want a secondary sort field, add a ThenBy expression to the chain.  Want a third level sort?  Just add ThenBy along with another sort expression. var projects = new List<Project>     {         new Project {Description = "A", ProjectStatusTypeId = 1},         new Project {Description = "B", ProjectStatusTypeId = 3},         new Project {Description = "C", ProjectStatusTypeId = 3},         new Project {Description = "C", ProjectStatusTypeId = 2},         new Project {Description = "E", ProjectStatusTypeId = 1},         new Project {Description = "A", ProjectStatusTypeId = 2},         new Project {Description = "C", ProjectStatusTypeId = 4},         new Project {Description = "A", ProjectStatusTypeId = 3}     };   projects = projects     .OrderBy(x => x.Description)     .ThenBy(x => x.ProjectStatusTypeId)     .ToList();   foreach (var project in projects) {     Console.Out.WriteLine("{0} {1}", project.Description,         project.ProjectStatusTypeId); } Linq offers a great sort solution most of the time, but what if you want or need to do it the old fashioned way? projects.Sort ((x, y) =>         Comparer<String>.Default             .Compare(x.Description, y.Description) != 0 ?         Comparer<String>.Default             .Compare(x.Description, y.Description) :         Comparer<Int32>.Default             .Compare(x.ProjectStatusTypeId, y.ProjectStatusTypeId));   foreach (var project in projects) {     Console.Out.WriteLine("{0} {1}", project.Description,         project.ProjectStatusTypeId); } It’s not that bad, right? Just for fun, let add some additional logic to our sort.  Let’s say we wanted our secondary sort to be based on the name associated with the ProjectStatusTypeId.  projects.Sort((x, y) =>        Comparer<String>.Default             .Compare(x.Description, y.Description) != 0 ?        Comparer<String>.Default             .Compare(x.Description, y.Description) :        Comparer<String>.Default             .Compare(GetProjectStatusTypeName(x.ProjectStatusTypeId),                 GetProjectStatusTypeName(y.ProjectStatusTypeId)));   foreach (var project in projects) {     Console.Out.WriteLine("{0} {1}", project.Description,         GetProjectStatusTypeName(project.ProjectStatusTypeId)); } The comparer will now consider the result of the GetProjectStatusTypeName and order the list accordingly.  Of course, you can take this same approach with Linq as well.

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  • Modifying Service URLs with LINQ to Twitter

    - by Joe Mayo
    It’s funny that two posts so close together speak about flexibility with the LINQ to Twitter provider.  There are certain things you know from experience on when to make software more flexible and when to save time.  This is another one of those times when I got lucky and made the right choice up front. I’m talking about the ability to switch URLs. It only makes sense that Twitter should begin versioning their API as it matures.  In fact, most of the entire API has moved to the v1 URL at “https://api.twitter.com/1/”, except for search and trends.  Recently, Twitter introduced the available and local trends, but hung them off the new v1, and left the rest of the trends API on the old URL. To implement this, I muscled my way into the expression tree during CreateRequestProcessor to figure out which trend I was dealing with; perhaps not elegant, but the code is in the right place and that’s what factories are for.  Anyway, the point is that I wouldn’t have to do this kind of stuff (as much fun as it is), if Twitter would have more consistency. Having went to Chirp last week and seeing the evolution of the API, it looks like my wish is coming true.  …now if they would just get their stuff together on the mess they made with geo-location and places… but again, that’s all transparent if your using LINQ to Twitter because I pulled all of that together in a consistent way so that you don’t have to. Normally, when Twitter makes a change, code breaks and I have to scramble to get the fixes in-place.  This time, in the case of a URL change, the adjustment is easy and no-one has to wait for me.  Essentially, all you need to do is change the URL passed to the TwitterContext constructor.  Here’s an example of instantiating a TwitterContext now: using (var twitterCtx = new TwitterContext(auth, "https://api.twitter.com/1/", "https://search.twitter.com/")) The third parameter constructor is the SearchUrl, which is used for Search and Trend APIs. You probably know what’s coming next; another constructor, but with the SearchUrl parameter set to the new URL as follows: using (var twitterCtx = new TwitterContext(auth, "https://api.twitter.com/1/", "https://api.twitter.com/1/")) One consequence of setting the URL this way is that you set the URL for both Trends and Search.  Since Search is still using the old URL, this is going to break for Search queries. You could always instantiate a special TwitterContext instance for Search queries, with the old URL set. Alternatively, you can use the TwitterContext’s SearchUrl property. Here’s an example: twitterCtx.SearchUrl = "https://api.twitter.com/1/"; var trends = (from trend in twitterCtx.Trends where trend.Type == TrendType.Daily && trend.Date == DateTime.Now.AddDays(-2).Date select trend) .ToList(); Notice how I set the SearchUrl property just-in-time for the query. This allows you to target the URL for each specific query. Whichever way you prefer to configure the URL, it’s your choice. So, now you know how to set the URL to be used for Trend queries and how to prevent whacking your Search queries. I’ll be updating the Trend API to use same URL as all other APIs soon, so the only API left to use the SearchUrl will be Search, but for the short term, it’s Trends and Search. Until I make this change, you’ll have a viable work-around by setting the URL yourself, as explained above. These were the Search and Trend URLs, but you might be curious about the second parameter of the TwitterContext constructor; that’s the URL for all other APIs (the BaseUrl), except for Trend and Search. Similarly, you can use the TwitterContext’s BaseUrl property to set the BaseUrl. Setting the BaseUrl can be useful when communicating with other services. In addition to Twitter changing URLs, the Twitter API has been adopted by other companies, such as Identi.ca, Tumblr, and  WordPress.  This capability lets you use LINQ to Twitter with any of these services.  This is a testament to the success of the Twitter API and it’s popularity. No doubt we’ll have hills and valleys to traverse as the Twitter API matures, but hopefully there will be enough flexibility in LINQ to Twitter to make these changes as transparent as possible for you. @JoeMayo

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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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  • LINQ and ArcObjects

    - by Marko Apfel
    Motivation LINQ (language integrated query) is a component of the Microsoft. NET Framework since version 3.5. It allows a SQL-like query to various data sources such as SQL, XML etc. Like SQL also LINQ to SQL provides a declarative notation of problem solving – i.e. you don’t need describe in detail how a task could be solved, you describe what to be solved at all. This frees the developer from error-prone iterator constructs. Ideally, of course, would be to access features with this way. Then this construct is conceivable: var largeFeatures = from feature in features where (feature.GetValue("SHAPE_Area").ToDouble() > 3000) select feature; or its equivalent as a lambda expression: var largeFeatures = features.Where(feature => (feature.GetValue("SHAPE_Area").ToDouble() > 3000)); This requires an appropriate provider, which manages the corresponding iterator logic. This is easier than you might think at first sight - you have to deliver only the desired entities as IEnumerable<IFeature>. LINQ automatically establishes a state machine in the background, whose execution is delayed (deferred execution) - when you are really request entities (foreach, Count (), ToList (), ..) an instantiation processing takes place, although it was already created at a completely different place. Especially in multiple iteration through entities in the first debuggings you are rubbing your eyes when the execution pointer jumps magically back in the iterator logic. Realization A very concise logic for constructing IEnumerable<IFeature> can be achieved by running through a IFeatureCursor. You return each feature via yield. For an easier usage I have put the logic in an extension method Getfeatures() for IFeatureClass: public static IEnumerable<IFeature> GetFeatures(this IFeatureClass featureClass, IQueryFilter queryFilter, RecyclingPolicy policy) { IFeatureCursor featureCursor = featureClass.Search(queryFilter, RecyclingPolicy.Recycle == policy); IFeature feature; while (null != (feature = featureCursor.NextFeature())) { yield return feature; } //this is skipped in unit tests with cursor-mock if (Marshal.IsComObject(featureCursor)) { Marshal.ReleaseComObject(featureCursor); } } So you can now easily generate the IEnumerable<IFeature>: IEnumerable<IFeature> features = _featureClass.GetFeatures(RecyclingPolicy.DoNotRecycle); You have to be careful with the recycling cursor. After a delayed execution in the same context it is not a good idea to re-iterated on the features. In this case only the content of the last (recycled) features is provided and all the features are the same in the second set. Therefore, this expression would be critical: largeFeatures.ToList(). ForEach(feature => Debug.WriteLine(feature.OID)); because ToList() iterates once through the list and so the the cursor was once moved through the features. So the extension method ForEach() always delivers the same feature. In such situations, you must not use a recycling cursor. Repeated executions of ForEach() is not a problem, because for every time the state machine is re-instantiated and thus the cursor runs again - that's the magic already mentioned above. Perspective Now you can also go one step further and realize your own implementation for the interface IEnumerable<IFeature>. This requires that only the method and property to access the enumerator have to be programmed. In the enumerator himself in the Reset() method you organize the re-executing of the search. This could be archived with an appropriate delegate in the constructor: new FeatureEnumerator<IFeatureclass>(_featureClass, featureClass => featureClass.Search(_filter, isRecyclingCursor)); which is called in Reset(): public void Reset() { _featureCursor = _resetCursor(_t); } In this manner, enumerators for completely different scenarios could be implemented, which are used on the client side completely identical like described above. Thus cursors, selection sets, etc. merge into a single matter and the reusability of code is increasing immensely. On top of that in automated unit tests an IEnumerable could be mocked very easily - a major step towards better software quality. Conclusion Nevertheless, caution should be exercised with these constructs in performance-relevant queries. Because of managing a state machine in the background, a lot of overhead is created. The processing costs additional time - about 20 to 100 percent. In addition, working without a recycling cursor is fast a performance gap. However declarative LINQ code is much more elegant, flawless and easy to maintain than manually iterating, compare and establish a list of results. The code size is reduced according to experience an average of 75 to 90 percent! So I like to wait a few milliseconds longer. As so often it has to be balanced between maintainability and performance - which for me is gaining in priority maintainability. In times of multi-core processors, the processing time of most business processes is anyway not dominated by code execution but by waiting for user input. Demo source code The source code for this prototype with several unit tests, you can download here: https://github.com/esride-apf/Linq2ArcObjects. .

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  • Another Linq to SQL product, Enzo Multitenant Framework

    - by Ed Gnatiuk
    An open source library and full product have been developed for transparently splitting large tables across several databases for performance, similar to database table partitioning.  It is all handled along with the Linq to SQL framework, and looks pretty slick, I will be reviewing the product shortly.  It looks mostly transparent to the developer!  There are other capabilites worth a look.  This looks like it works for azure as well. Here are some links:  http://enzosqlshard.codeplex.com/   http://enzosqlbaseline.com    https://scale.bluesyntax.net   I will be reviewing this and other Linq to SQL libraries soon.

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  • Track updated/inserted entities in LINQ to SQL applications

    - by nikolaosk
    In this post I would like to discuss in further detail the issue of track changing of entities in LINQ to SQL applications. I would like to show you how the DataContext object keeps track of all the items that are updated,deleted or inserted in the underlying data store. If you want to have a look at my other post about LINQ to SQL and transactions click here . I am going to demonstrate this with a hands on example. I assume that you have access to a version of SQL Server and Northwind database....(read more)

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  • Rake don't know how to build task?

    - by Schroedinger
    Using a rake task to import data into a database: file as follows namespace :db do desc "load imported data from csv" task :load_csv_data => :environment do require 'fastercsv' require 'chronic' FasterCSV.foreach("input.csv", :headers => true) do |row| Trade.create( :name => row[0], :type => row[4], :price => row[6].to_f, :volume => row[7].to_i, :bidprice => row[10].to_f, :bidsize => row[11].to_i, :askprice => row[14].to_f, :asksize => row[15].to_i ) end end end When attempting to use this, with the right CSV files and the other elements in place, it will say Don't know how to build task 'db:import_csv_data' I know this structure works because I've tested it, I'm just trying to get it to convert to the new values on the fly. Suggestions?

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  • Dynamically generating a file with javascript?

    - by gct
    I'm working on a web app for my company that will let us do some image tagging stuff, and I'd like to be able to generates results in the form of a CSV file. I can do this easily enough by dumping the CSV data to a div or something on the page and having the user copy it out. I'd rather have them hit the a generate button and have a CSV file downloaded as though they clicked on a link to the result, so they can more easily just save the file somewhere convenient. Is it possible to simulate this kind of thing with javascript? I basically want to dynamically generate the file and then let them download it, client side.

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  • How to view a DataTable while debuging

    - by Eric
    I'm just getting started using ADO.NET and DataSets and DataTables. One problem I'm having is it seems pretty hard to tell what values are in the data table when trying to debug. What are some of the easiest ways of quickly seeing what values have been saved in a DataTable? Is there someway to see the contents in Visual Studio while debugging or is the only option to write the data out to a file? I've created a little utility function that will write a DataTable out to a CSV file. Yet the the resulting CSV file created was cut off. About 3 lines from what should have been the last line in the middle of writing out a System.Guid the file just stops. I can't tell if this is an issue with my CSV conversion method, or the original population of the DataTable. Update Forget the last part I just forgot to flush my stream writer.

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  • Efficient way to access a mapping of identifiers in Python

    - by sixbelo
    I am writing an app to do a file conversion and part of that is replacing old account numbers with a new account numbers. Right now I have a CSV file mapping the old and new account numbers with around 30K records. I read this in and store it as dict and when writing the new file grab the new account from the dict by key. My question is what is the best way to do this if the CSV file increases to 100K+ records? Would it be more efficient to convert the account mappings from a CSV to a sqlite database rather than storing them as a dict in memory?

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  • Creating interruptible process in python

    - by Glycerine
    I'm creating a python script of which parses a large (but simple) CSV. It'll take some time to process. I would like the ability to interrupt the parsing of the CSV so I can continue at a later stage. Currently I have this - of which lives in a larger class: (unfinished) Edit: I have some changed code. But the system will parse over 3 million rows. def parseData(self) reader = csv.reader(open(self.file)) for id, title, disc in reader: print "%-5s %-50s %s" % (id, title, disc) l = LegacyData() l.old_id = int(id) l.name = title l.disc_number = disc l.parsed = False l.save() This is the old code. def parseData(self): #first line start fields = self.data.next() for row in self.data: items = zip(fields, row) item = {} for (name, value) in items: item[name] = value.strip() self.save(item) Thanks guys.

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  • The null value cannot be assigned to a member with type System.Int64 which is a non-nullable value t

    - by BritishDeveloper
    I'm getting the following error in my MVC2 app using Linq to SQL (I am new to both). I am connected to an actual SQL server not weird mdf: System.InvalidOperationException The null value cannot be assigned to a member with type System.Int64 which is a non-nullable value type My SQL table has a column called MessageID. It is BigInt type and has a primary key, NOT NULL and an IDENTITY 1 1, no Default In my dbml designer it has the following declaration for this field: [global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_MessageId", AutoSync=AutoSync.OnInsert, DbType="BigInt NOT NULL IDENTITY", IsPrimaryKey=true, IsDbGenerated=true)] public long MessageId { get { return this._MessageId; } set { if ((this._MessageId != value)) { this.OnMessageIdChanging(value); this.SendPropertyChanging(); this._MessageId = value; this.SendPropertyChanged("MessageId"); this.OnMessageIdChanged(); } } } It keeps telling me that null cannot be assigned - I'm not passing through null! It's a long - it can't even be null! Am I doing something stupid? I can't find a solution anywhere! I made this work by changing the type of this property to Nullable<long> but surely this can't be right? Update: I am using InsertOnSubmit. Simplified code: public ActionResult Create(Message message) { if (ModelState.IsValid) { var db = new MessagingDataContext(); db.Messages.InsertOnSubmit(message); db.SubmitChanges(); //line 93 (where it breaks) } } breaks on SubmitChanges() with the error at the top of this question. Update2: Stack trace: at Read_Object(ObjectMaterializer`1 ) at System.Data.Linq.SqlClient.ObjectReaderCompiler.ObjectReader`2.MoveNext() at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source) at System.Data.Linq.ChangeDirector.StandardChangeDirector.DynamicInsert(TrackedObject item) at System.Data.Linq.ChangeDirector.StandardChangeDirector.Insert(TrackedObject item) at System.Data.Linq.ChangeProcessor.SubmitChanges(ConflictMode failureMode) at System.Data.Linq.DataContext.SubmitChanges(ConflictMode failureMode) at Qanda.Controllers.MessagingController.Ask(Message message) in C:\Qanda\Qanda\Controllers\MessagingController.cs:line 93 Update3: No one knows and I don't have enough clout to offer a bounty! So continued on my ASP.NET blog. Please help!

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