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• See if item exists once in Enumerable (Linq)

  - by Stacey

  Given a list... class Item { public Name { get; set; } } List<Item> items = new List<Item> { new Item() { Name = "Item 1" }, new Item() { Name = "Item 1" }, new Item() { Name = "Item 2" }, new Item() { Name = "Item 3" } } List<Item> listing = new List<Item> { new Item() { Name = "Item 1" }, new Item() { Name = "Item 2" }, new Item() { Name = "Item 3" } new Item() { Name = "Item 4" } } etc. I need to create a third array that will cancel out double instances between the two; however items with "Name 1" are both the same, but different 'instances'. So the third List should have 1 instance of Item 1, since 'items' had 2 instances. Any ideas of how this can be done through Linq?

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• How to stop PowerShell from unpacking an Enumerable object?

  - by spoon16

  Working on a simple helper function in PowerShell that takes a couple of parameters and creates a custom Enumerable object and outputs that object to the pipeline. The problem I am having is that PowerShell is always outputting a System.Array that contains the objects that are enumerated by my custom Enumerable object. How can I keep PowerShell from unpacking the Enumerable object? The code: http://gist.github.com/387768

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• How to iterate multiple enumerables in ruby?

  - by steenslag

  I know two arrays can be zipped and the result can be iterated with #each. But how do you do it with an unknown number of enumerables? Let's say anand = &w(1-0 0.5-0.5 0.5-0.5 1.0) carlsen = &w(0-1 0.5-0.5 0.5-0.5 1.0) kramnik = &w(0.5-0.5 0.5-0.5 0.5-0.5 1.0) players= [anand, carlsen, kramnik) #something smart players.each{|round|puts round} #first line should be "1-0 0-1 0.5-0.5"

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• IEnumerable doesn't have Count

  - by Alexander

  I have the following method: public bool IsValid { get { return (GetRuleViolations().Count() == 0); } } public IEnumerable<RuleViolation> GetRuleViolations(){ //code here } Why is it that when I do .Count above it is underlined in red? I got the following error: Error 1 'System.Collections.Generic.IEnumerable' does not contain a definition for 'Count' and no extension method 'Count' accepting a first argument of type 'System.Collections.Generic.IEnumerable' could be found (are you missing a using directive or an assembly reference?) c:\users\a\documents\visual studio 2010\Projects\NerdDinner\NerdDinner\Models\Dinner.cs 15 47 NerdDinner

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• rails - when using Group_by - How to get an Index?

  - by AnApprentice

  I have the following: sets = DataSet.all.group_by{ |data| [data.project_id, "-", data.thread_id].join(" ") } <% sets.each do |range, datas| %> <p><%= range %>:</p> <% datas.each do |data| %> <%=data%> <p>Last Post<%= data.last.created_at %></p> <% end %> <% end %> Problem is that I need an index. So i updated the above with: <% sets.each_with_index do |range, datas, i| %> <p><%= range %>:</p> <% datas.each do |data| %> <%= i %> <%=data%> <p>Last Post<%= data.last.created_at %></p> <% end %> <% end %> That then breaks, with the error: undefined method `last' for 0:Fixnum Ideas? thank you

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• Clean solution to this ruby iterator trickiness?

  - by mstksg

  k = [1,2,3,4,5] for n in k puts n if n == 2 k.delete(n) end end puts k.join(",") # Result: # 1 # 2 # 4 # 5 # [1,3,4,5] # Desired: # 1 # 2 # 3 # 4 # 5 # [1,3,4,5] This same effect happens with the other array iterator, k.each: k = [1,2,3,4,5] k.each do |n| puts n if n == 2 k.delete(n) end end puts k.join(",") has the same output. The reason this is happening is pretty clear...Ruby doesn't actually iterate through the objects stored in the array, but rather just turns it into a pretty array index iterator, starting at index 0 and each time increasing the index until it's over. But when you delete an item, it still increments the index, so it doesn't evaluate the same index twice, which I want it to. This might not be what's happening, but it's the best I can think of. Is there a clean way to do this? Is there already a built-in iterator that can do this? Or will I have to dirty it up and do an array index iterator, and not increment when the item is deleted?

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• Calculate sum of objects for each unique object property in Ruby

  - by macek

  I was helping with an answer in this question and it sparked a question of my own. Pie is an object that has a pieces array made of of PiePiece objects. Each PiePiece has a flavor attribute How do I create a hash that looks like this: # flavor => number of pieces { :cherry => 3 :apple => 1 :strawberry => 2 } This works, but I think it could be improved def inventory hash = {} pieces.each do |p| hash[p.flavor] ||= 0 hash[p.flavor] += 1 end hash end Any ideas?

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• Ninject 2 for CF3.5 TargetInvocationException

  - by jack london

  In middle of application when calling following line: var component = _Kernel.Get<IComponent>(); I'm getting TargetInvocationException. IComponent is a Form. at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) at System.Reflection.ConstructorInfo.Invoke(Object[] parameters) at Ninject.Injection.ReflectionInjectorFactory.<c_DisplayClass1.b_0(Object[] args) at Ninject.Activation.Providers.StandardProvider.Create(IContext context) at Ninject.Activation.Context.Resolve() at Ninject.KernelBase.b_7(IContext context) at System.Linq.Enumerable.d_d2.MoveNext() at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable1 source) at Ninject.Planning.Targets.Target1.ResolveWithin(IContext parent) at Ninject.Activation.Providers.StandardProvider.GetValue(IContext context, ITarget target) at Ninject.Activation.Providers.StandardProvider.<>c__DisplayClass2.<Create>b__1(ITarget target) at System.Linq.Enumerable.<SelectIterator>d__d2.MoveNext() at System.Linq.Buffer1..ctor(IEnumerable1 source) at System.Linq.Enumerable.ToArray[TSource](IEnumerable1 source) at Ninject.Activation.Providers.StandardProvider.Create(IContext context) at Ninject.Activation.Context.Resolve() at Ninject.KernelBase.<Resolve>b__7(IContext context) at System.Linq.Enumerable.<SelectIterator>d__d2.MoveNext() at System.Linq.Enumerable.d__b01.MoveNext() at System.Linq.Enumerable.Single[TSource](IEnumerable1 source) at Ninject.ResolutionExtensions.Get[T](IResolutionRoot root, IParameter[] parameters)

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• Dynamic Paging and Sorting

  - by Ricardo Peres

  Since .NET 3.5 brought us LINQ and expressions, I became a great fan of these technologies. There are times, however, when strong typing cannot be used - for example, when you are developing an ObjectDataSource and you need to do paging having just a column name, a page index and a page size, so I set out to fix this. Yes, I know about Dynamic LINQ, and even talked on it previously, but there's no need to add this extra assembly. So, without further delay, here's the code, in both generic and non-generic versions: public static IList ApplyPagingAndSorting(IEnumerable enumerable, Type elementType, Int32 pageSize, Int32 pageIndex, params String [] orderByColumns) { MethodInfo asQueryableMethod = typeof(Queryable).GetMethods(BindingFlags.Static | BindingFlags.Public).Where(m = (m.Name == "AsQueryable") && (m.ContainsGenericParameters == false)).Single(); IQueryable query = (enumerable is IQueryable) ? (enumerable as IQueryable) : asQueryableMethod.Invoke(null, new Object [] { enumerable }) as IQueryable; if ((orderByColumns != null) && (orderByColumns.Length 0)) { PropertyInfo orderByProperty = elementType.GetProperty(orderByColumns [ 0 ]); MemberExpression member = Expression.MakeMemberAccess(Expression.Parameter(elementType, "n"), orderByProperty); LambdaExpression orderBy = Expression.Lambda(member, member.Expression as ParameterExpression); MethodInfo orderByMethod = typeof(Queryable).GetMethods(BindingFlags.Public | BindingFlags.Static).Where(m = m.Name == "OrderBy").ToArray() [ 0 ].MakeGenericMethod(elementType, orderByProperty.PropertyType); query = orderByMethod.Invoke(null, new Object [] { query, orderBy }) as IQueryable; if (orderByColumns.Length 1) { MethodInfo thenByMethod = typeof(Queryable).GetMethods(BindingFlags.Public | BindingFlags.Static).Where(m = m.Name == "ThenBy").ToArray() [ 0 ].MakeGenericMethod(elementType, orderByProperty.PropertyType); PropertyInfo thenByProperty = null; MemberExpression thenByMember = null; LambdaExpression thenBy = null; for (Int32 i = 1; i 0) { MethodInfo takeMethod = typeof(Queryable).GetMethod("Take", BindingFlags.Public | BindingFlags.Static).MakeGenericMethod(elementType); MethodInfo skipMethod = typeof(Queryable).GetMethod("Skip", BindingFlags.Public | BindingFlags.Static).MakeGenericMethod(elementType); query = skipMethod.Invoke(null, new Object [] { query, pageSize * pageIndex }) as IQueryable; query = takeMethod.Invoke(null, new Object [] { query, pageSize }) as IQueryable; } MethodInfo toListMethod = typeof(Enumerable).GetMethod("ToList", BindingFlags.Static | BindingFlags.Public).MakeGenericMethod(elementType); IList list = toListMethod.Invoke(null, new Object [] { query }) as IList; return (list); } public static List ApplyPagingAndSorting(IEnumerable enumerable, Int32 pageSize, Int32 pageIndex, params String [] orderByColumns) { return (ApplyPagingAndSorting(enumerable, typeof(T), pageSize, pageIndex, orderByColumns) as List); } List list = new List { new DateTime(2010, 1, 1), new DateTime(1999, 1, 12), new DateTime(1900, 10, 10), new DateTime(1900, 2, 20), new DateTime(2012, 5, 5), new DateTime(2012, 1, 20) }; List sortedList = ApplyPagingAndSorting(list, 3, 0, "Year", "Month", "Day"); SyntaxHighlighter.config.clipboardSwf = 'http://alexgorbatchev.com/pub/sh/2.0.320/scripts/clipboard.swf'; SyntaxHighlighter.brushes.CSharp.aliases = ['c#', 'c-sharp', 'csharp']; SyntaxHighlighter.all();

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• Dynamic Filtering

  - by Ricardo Peres

  Continuing my previous posts on dynamic LINQ, now it's time for dynamic filtering. For now, I'll focus on string matching. There are three standard operators for string matching, which both NHibernate, Entity Framework and LINQ to SQL recognize: Equals Contains StartsWith EndsWith So, if we want to apply filtering by one of these operators on a string property, we can use this code: public enum MatchType { StartsWith = 0, EndsWith = 1, Contains = 2, Equals = 3 } public static List Filter(IEnumerable enumerable, String propertyName, String filter, MatchType matchType) { return (Filter(enumerable, typeof(T), propertyName, filter, matchType) as List); } public static IList Filter(IEnumerable enumerable, Type elementType, String propertyName, String filter, MatchType matchType) { MethodInfo asQueryableMethod = typeof(Queryable).GetMethods(BindingFlags.Static | BindingFlags.Public).Where(m = (m.Name == "AsQueryable") && (m.ContainsGenericParameters == false)).Single(); IQueryable query = (enumerable is IQueryable) ? (enumerable as IQueryable) : asQueryableMethod.Invoke(null, new Object [] { enumerable }) as IQueryable; MethodInfo whereMethod = typeof(Queryable).GetMethods(BindingFlags.Public | BindingFlags.Static).Where(m = m.Name == "Where").ToArray() [ 0 ].MakeGenericMethod(elementType); MethodInfo matchMethod = typeof(String).GetMethod ( (matchType == MatchType.StartsWith) ? "StartsWith" : (matchType == MatchType.EndsWith) ? "EndsWith" : (matchType == MatchType.Contains) ? "Contains" : "Equals", new Type [] { typeof(String) } ); PropertyInfo displayProperty = elementType.GetProperty(propertyName, BindingFlags.Public | BindingFlags.Instance); MemberExpression member = Expression.MakeMemberAccess(Expression.Parameter(elementType, "n"), displayProperty); MethodCallExpression call = Expression.Call(member, matchMethod, Expression.Constant(filter)); LambdaExpression where = Expression.Lambda(call, member.Expression as ParameterExpression); query = whereMethod.Invoke(null, new Object [] { query, where }) as IQueryable; MethodInfo toListMethod = typeof(Enumerable).GetMethod("ToList", BindingFlags.Static | BindingFlags.Public).MakeGenericMethod(elementType); IList list = toListMethod.Invoke(null, new Object [] { query }) as IList; return (list); } var list = new [] { new { A = "aa" }, new { A = "aabb" }, new { A = "ccaa" }, new { A = "ddaadd" } }; var contains = Filter(list, "A", "aa", MatchType.Contains); var endsWith = Filter(list, "A", "aa", MatchType.EndsWith); var startsWith = Filter(list, "A", "aa", MatchType.StartsWith); var equals = Filter(list, "A", "aa", MatchType.Equals); Perhaps I'll write some more posts on this subject in the near future. SyntaxHighlighter.config.clipboardSwf = 'http://alexgorbatchev.com/pub/sh/2.0.320/scripts/clipboard.swf'; SyntaxHighlighter.brushes.CSharp.aliases = ['c#', 'c-sharp', 'csharp']; SyntaxHighlighter.all();

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• How to find out if an object's type implements IEnumerable<X> where X derives from Base using Reflec

  - by Dave Van den Eynde

  Give a base class "Base", I want to write a method Test, like this: private static bool Test(IEnumerable enumerable) { ... } such that Test returns true if the type of o implements any interface of IEnumerable where X derives from Base, so that if I would do this: public static IEnumerable<string> Convert(IEnumerable enumerable) { if (Test(enumerable)) { return enumerable.Cast<Base>().Select(b => b.SomePropertyThatIsString); } return enumerable.Cast<object>().Select(o => o.ToString()); } ...that it would do the right thing, using Reflection. I'm sure that its a matter of walking across all the interfaces of the type to find the first that matches the requirements, but I'm having a hard time finding the generic IEnumerable< among them. Of course, I could consider this: public static IEnumerable<string> Convert(IEnumerable enumerable) { return enumerable.Cast<object>().Select(o => o is Base ? ((Base)o).SomePropertyThatIsString : o.ToString()); } ...but think of it as a thought experiment.

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• Just wondering what is the reason of InvalidOperationException in Enumerable.Aggregate<TSource>?

  - by the_joric

  Why only one overload throws this exception?

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• What is the advantage of creating an enumerable object using to_enum in Ruby?

  - by Jason

  Hi, Why would you create a proxy reference to an object in Ruby, by using the to_enum method rather than just using the object directly? I cannot think of any practical use for this, trying to understand this concept & where someone might use it, but all the examples I have seen seem very trivial. For example, why use: "hello".enum_for(:each_char).map {|c| c.succ } instead of "hello".each_char.map {|c| c.succ } I know this is a very simple example, does anyone have any real-world examples? Thanks!

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• LINQ: GroupBy with maximum count in each group

  - by polarbear2k

  Hi, I have a list of duplicate numbers: Enumerable.Range(1,3).Select(o => Enumerable.Repeat(o, 3)).SelectMany(o => o) // {1,1,1,2,2,2,3,3,3} I group them and get quantity of occurance: Enumerable.Range(1,3).Select(o => Enumerable.Repeat(o, 3)).SelectMany(o => o) .GroupBy(o => o).Select(o => new { Qty = o.Count(), Num = o.Key }) Qty Num 3 1 3 2 3 3 What I really need is to limit the quantity per group to some number. If the limit is 2 the result for the above grouping would be: Qty Num 2 1 1 1 2 2 1 2 2 3 1 3 So, if Qty = 10 and limit is 4, the result is 3 rows (4, 4, 2). The Qty of each number is not equal like in example. The specified Qty limit is the same for whole list (doesn't differ based on number). Thanks

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• Existing LINQ extension method similar to Parallel.For?

  - by Joel Martinez

  The linq extension methods for ienumerable are very handy ... but not that useful if all you want to do is apply some computation to each item in the enumeration without returning anything. So I was wondering if perhaps I was just missing the right method, or if it truly doesn't exist as I'd rather use a built-in version if it's available ... but I haven't found one :-) I could have sworn there was a .ForEach method somewhere, but I have yet to find it. In the meantime, I did write my own version in case it's useful for anyone else: using System.Collections; using System.Collections.Generic; public delegate void Function<T>(T item); public delegate void Function(object item); public static class EnumerableExtensions { public static void For(this IEnumerable enumerable, Function func) { foreach (object item in enumerable) { func(item); } } public static void For<T>(this IEnumerable<T> enumerable, Function<T> func) { foreach (T item in enumerable) { func(item); } } } usage is: myEnumerable.For<MyClass>(delegate(MyClass item) { item.Count++; });

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• C# Tupel group limitation

  - by user609511

  How can i controll the loop of Tupel Repeatation ? Someone has give me a hint about my algorithm. I modified a little bit his algorithm. int LimCol = Convert.ToInt32(LimitColis); result = oListTUP .GroupBy(x => x.Item1) .Select(g => new { Key = g.Key, Sum = g.Sum(x => x.Item2), Poids = g.Sum(x => x.Item3), }) .Select(p => new { Key = p.Key, Items = Enumerable.Repeat(LimCol , p.Sum / LimCol).Concat(Enumerable.Repeat(p.Sum % LimCol, 1)), CalculPoids = p.Poids / (Enumerable.Repeat(LimCol, p.Sum / LimCol).Concat(Enumerable.Repeat(p.Sum % LimCol, 1))).Count() }) .SelectMany(p => p.Items.Select(i => Tuple.Create(p.Key, i, p.CalculPoids))) .ToList(); foreach (var oItem in result) { Label1.Text += oItem.Item1 + "--" + oItem.Item2 + "--" + oItem.Item3 + "<br>"; } the result with LimCol = 3 as you can see i colored with red is the problem. i expected: 0452632--3--3,75 0452632--3--3,75 0452632--3--3,75 0452632--3--3,75 essai 49--3--79,00 essai 49--2--79,00 Thanks you in advance

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• LINQ to SQL Converter

  - by user609511

  How can I convert My LINQ to SQL ? i have this LINQ statement: int LimCol = Convert.ToInt32(LimitColis); result = oListTUP .GroupBy(x => new { x.Item1, x.Item2, x.Item3, x.Item4, x.Item5 }) .Select(g => new { Key = g.Key, Sum = g.Sum(x => x.Item6), Poids = g.Sum(x => x.Item7), }) .Select(p => new { Key = p.Key, Items = Enumerable.Repeat(LimCol, p.Sum / LimCol).Concat(Enumerable.Repeat(p.Sum % LimCol, p.Sum % LimCol > 0 ? 1 : 0)), CalculPoids = p.Poids / Enumerable.Repeat(LimCol, p.Sum / LimCol).Concat(Enumerable.Repeat(p.Sum % LimCol, p.Sum % LimCol > 0 ? 1 : 0)).Count() }) .SelectMany(p => p.Items.Select(i => Tuple.Create(p.Key.Item1, p.Key.Item2, p.Key.Item3, p.Key.Item4, p.Key.Item5, i, p.CalculPoids))) .ToList(); } It works well, but somehow want to push it and it become too complicated, so I want to convert it into Pure SQL. I have tried SQL Profiler and LinqPad, but neither shows me the SQL. How can I see the SQL code from My LINQ ? Thank you in advance.

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• Why does calling IEnumerable<string>.Count() create an additional assembly dependency ?

  - by Gishu

  Assume this chain of dll references Tests.dll >> Automation.dll >> White.Core.dll with the following line of code in Tests.dll, where everything builds result.MissingPaths Now when I change this to result.MissingPaths.Count() I get the following build error for Tests.dll "White.UIItem is not defined in an assembly that is not referenced. You must add a reference to White.Core.dll." And I don't want to do that because it breaks my layering. Here is the type definition for result, which is in Automation.dll public class HasResult { public HasResult(IEnumerable<string> missingPaths ) { MissingPaths = missingPaths; } public IEnumerable<string> MissingPaths { get; set; } public bool AllExist { get { return !MissingPaths.Any(); } } } Down the call chain the input param to this ctor is created via (The TreeNode class is in White.Core.dll) assetPaths.Where(assetPath => !FindTreeNodeUsingCache(treeHandle, assetPath)); Why does this dependency leak when calling Count() on IEnumerable ? I then suspected that lazy evaluation was causing this (for some reason) - so I slotted in an ToArray() in the above line but didn't work. Update 2011 01 07: Curiouser and Curiouser! it won't build until I add a White.Core reference. So I add a reference and build it (in order to find the elusive dependency source). Open it up in Reflector and the only references listed are Automation, mscorlib, System.core and NUnit. So the compiler threw away the White reference as it was not needed. ILDASM also confirms that there is no White AssemblyRef entry. Any ideas on how to get to the bottom of this thing (primarily for 'now I wanna know why' reasons)? What are the chances that this is an VS2010/MSBuild bug? Update 2011 01 07 #2 As per Shimmy's suggestion, tried calling the method explcitly as an extension method Enumerable.Count(result.MissingPaths) and it stops cribbing (not sure why). However I moved some code around after that and now I'm getting the same issue at a different location using IEnumerable - this time reading and filtering lines out of a file on disk (totally unrelated to White). Seems like it's a 'symptom-fix'. var lines = File.ReadLines(aFilePath).ToArray(); once again, if I remove the ToArray() it compiles again - it seems that any method that causes the enumerable to be evaluated (ToArray, Count, ToList, etc.) causes this. Let me try and get a working tiny-app to demo this issue... Update 2011 01 07 #3 Phew! More information.. It turns out the problem is just in one source file - this file is LINQ-phobic. Any call to an Enumerable extension method has to be explicitly called out. The refactorings that I did caused a new method to be moved into this source file, which had some LINQ :) Still no clue as to why this class dislikes LINQ. using System; using System.Collections.Generic; using System.IO; using System.Linq; using G.S.OurAutomation.Constants; using G.S.OurAutomation.Framework; using NUnit.Framework; namespace G.S.AcceptanceTests { public abstract class ConfigureThingBase : OurTestFixture { .... private static IEnumerable<string> GetExpectedThingsFor(string param) { // even this won't compile - although it compiles fine in an adjoining source file in the same assembly //IEnumerable<string> s = new string[0]; //Console.WriteLine(s.Count()); // this is the line that is now causing a build failure // var expectedInfo = File.ReadLines(someCsvFilePath)) // .Where(line => !line.StartsWith("REM", StringComparison.InvariantCultureIgnoreCase)) // .Select(line => line.Replace("%PLACEHOLDER%", param)) // .ToArray(); // Unrolling the LINQ above removes the build error var expectedInfo = Enumerable.ToArray( Enumerable.Select( Enumerable.Where( File.ReadLines(someCsvFilePath)), line => !line.StartsWith("REM", StringComparison.InvariantCultureIgnoreCase)), line => line.Replace("%PLACEHOLDER%", param)));

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• System.Interactive: Difference between Memoize() and MemoizeAll()?

  - by Joel Mueller

  In System.Interactive.dll (v1.0.2521.0) from Reactive Extensions, EnumerableEx has both a Memoize method and a MemoizeAll method. The API documentation is identical for both of them: Creates an enumerable that enumerates the original enumerable only once and caches its results. However, these methods are clearly not identical. If I use Memoize, my enumerable has values the first time I enumerate it, and seems to be empty the second time. If I use MemoizeAll then I get the behavior I would expect from the description of either method - I can enumerate the result as many times as I want and get the same results each time, but the source is only enumerated once. Can anyone tell me what the intended difference between these methods is? What is the use-case for Memoize? It seems like a fairly useless method with really confusing documentation.

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• What is wrong with the below statement(C#3.0 / Lambda)

  - by Newbie

  what is wrong in the below Enumerable.Range(0, objEntityCode.Count - 1).Select(i => { options.Attributes[i] = new EntityCodeKey { EntityCode = objEntityCode[i].EntityCodes , OrganizationCode = Constants.ORGANIZATION_CODE }; }) .ToArray(); Throwing error The type arguments for method 'System.Linq.Enumerable.Select(System.Collections.Generic.IEnumerable, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly. But this works Enumerable.Range(0, objEntityCode.Count - 1).ToList().ForEach(i => { options.Attributes[i] = new EntityCodeKey { EntityCode = objEntityCode[i].EntityCodes , OrganizationCode = Constants.ORGANIZATION_CODE }; } ); Using C#3.0. Purpose: I am learning LINQ / LAMBDA and trying to do the same program in different way. Thanks.

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• LINQ and the use of Repeat and Range operator

  - by vik20000in

  LINQ is also very useful when it comes to generation of range or repetition of data.  We can generate a range of data with the help of the range method.     var numbers =         from n in Enumerable.Range(100, 50)         select new {Number = n, OddEven = n % 2 == 1 ? "odd" : "even"}; The above query will generate 50 records where the record will start from 100 till 149. The query also determines if the number is odd or even. But if we want to generate the same number for multiple times then we can use the Repeat method.     var numbers = Enumerable.Repeat(7, 10); The above query will produce a list with 10 items having the value 7. Vikram

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• Challenge: Neater way of currying or partially applying C#4's string.Join

  - by Damian Powell

  Background I recently read that .NET 4's System.String class has a new overload of the Join method. This new overload takes a separator, and an IEnumerable<T> which allows arbitrary collections to be joined into a single string without the need to convert to an intermediate string array. Cool! That means I can now do this: var evenNums = Enumerable.Range(1, 100) .Where(i => i%2 == 0); var list = string.Join(",",evenNums); ...instead of this: var evenNums = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .Select(i => i.ToString()) .ToArray(); var list = string.Join(",", evenNums); ...thus saving on a conversion of every item to a string, and then the allocation of an array. The Problem However, being a fan of the functional style of programming in general, and method chaining in C# in particular, I would prefer to be able to write something like this: var list = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .string.Join(","); This is not legal C# though. The closest I've managed to get is this: var list = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .ApplyTo( Functional.Curry<string, IEnumerable<object>, string> (string.Join)(",") ); ...using the following extension methods: public static class Functional { public static TRslt ApplyTo<TArg, TRslt>(this TArg arg, Func<TArg, TRslt> func) { return func(arg); } public static Func<T1, Func<T2, TResult>> Curry<T1, T2, TResult>(this Func<T1, T2, TResult> func) { Func<Func<T1, T2, TResult>, Func<T1, Func<T2, TResult>>> curried = f => x => y => f(x, y); return curried(func); } } This is quite verbose, requires explicit definition of the parameters and return type of the string.Join overload I want to use, and relies upon C#4's variance features because we are defining one of the arguments as IEnumerable rather than IEnumerable. The Challenge Can you find a neater way of achieving this using the method-chaining style of programming?

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• How to detect if a LINQ enumeration is materialized?

  - by Peter Lillevold

  Is there some way of detecting whether an enumerable built using LINQ (to Objects in this case) have been materialized or not? Other than trying to inspect the type of the underlying collection? Specifically, since enumerable.ToArray() will build a new array even if the underlying collection already is an array I'm looking for a way of avoiding ToArray() being called twice on the same collection.

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• C# - AsEnumerable Example

  - by udanamehar

  What is the exact use of AsEnumerable? Will it change non-enumerable collection to enumerable collection?.Please give me a simple example.

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• Gnome Do not Launching

  - by PyRulez

  When I try running gnome do, I get this. chris@Chris-Ubuntu-Laptop:~$ gnome-do pgrep: invalid user name: -u and it is not writable Trying sudo: chris@Chris-Ubuntu-Laptop:~$ sudo gnome-do [NetworkService] Could not initialize Network Manager dbus: Unable to open the session message bus. [Error 17:54:30.122] [SystemService] Could not initialize dbus: Unable to open the session message bus. (Do:2401): Wnck-CRITICAL **: wnck_set_client_type got called multiple times. (Do:2401): libdo-WARNING **: Binding '<Super>space' failed! [Error 17:54:30.649] [AbstractKeyBindingService] Key "" is already mapped. Tomboy.NotesItemSource "Tomboy Notes" encountered an error in UpdateItems: System.TypeInitializationException: An exception was thrown by the type initializer for Tomboy.TomboyDBus ---> System.Exception: Unable to open the session message bus. ---> System.ArgumentNullException: Argument cannot be null. Parameter name: address at NDesk.DBus.Bus.Open (System.String address) [0x00000] in <filename unknown>:0 at NDesk.DBus.Bus.get_Session () [0x00000] in <filename unknown>:0 --- End of inner exception stack trace --- at NDesk.DBus.Bus.get_Session () [0x00000] in <filename unknown>:0 at Tomboy.TomboyDBus..cctor () [0x00000] in <filename unknown>:0 --- End of inner exception stack trace --- at Tomboy.NotesItemSource.UpdateItems () [0x00000] in <filename unknown>:0 at Do.Universe.Safe.SafeItemSource.UpdateItems () [0x00000] in <filename unknown>:0 . Firefox.PlacesItemSource "Firefox Places" encountered an error in UpdateItems: System.InvalidCastException: Cannot cast from source type to destination type. at Mono.Data.Sqlite.SqliteDataReader.VerifyType (Int32 i, DbType typ) [0x00000] in <filename unknown>:0 at Mono.Data.Sqlite.SqliteDataReader.GetString (Int32 i) [0x00000] in <filename unknown>:0 at Firefox.PlacesItemSource+<LoadPlaceItems>c__Iterator3.MoveNext () [0x00000] in <filename unknown>:0 at System.Collections.Generic.List`1[Firefox.PlaceItem].AddEnumerable (IEnumerable`1 enumerable) [0x00000] in <filename unknown>:0 at System.Collections.Generic.List`1[Firefox.PlaceItem]..ctor (IEnumerable`1 collection) [0x00000] in <filename unknown>:0 at System.Linq.Enumerable.ToArray[PlaceItem] (IEnumerable`1 source) [0x00000] in <filename unknown>:0 at Firefox.PlacesItemSource.UpdateItems () [0x00000] in <filename unknown>:0 at Do.Universe.Safe.SafeItemSource.UpdateItems () [0x00000] in <filename unknown>:0 . Do.Universe.Linux.GNOMESpecialLocationsItemSource "GNOME Special Locations" encountered an error in UpdateItems: System.IO.FileNotFoundException: Could not find file "/root/.gtk-bookmarks". File name: '/root/.gtk-bookmarks' at System.IO.FileStream..ctor (System.String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, Boolean anonymous, FileOptions options) [0x00000] in <filename unknown>:0 at System.IO.FileStream..ctor (System.String path, FileMode mode, FileAccess access, FileShare share) [0x00000] in <filename unknown>:0 at (wrapper remoting-invoke-with-check) System.IO.FileStream:.ctor (string,System.IO.FileMode,System.IO.FileAccess,System.IO.FileShare) at System.IO.File.OpenRead (System.String path) [0x00000] in <filename unknown>:0 at System.IO.StreamReader..ctor (System.String path, System.Text.Encoding encoding, Boolean detectEncodingFromByteOrderMarks, Int32 bufferSize) [0x00000] in <filename unknown>:0 at System.IO.StreamReader..ctor (System.String path) [0x00000] in <filename unknown>:0 at (wrapper remoting-invoke-with-check) System.IO.StreamReader:.ctor (string) at Do.Universe.Linux.GNOMESpecialLocationsItemSource+<ReadBookmarkItems>c__Iterator3.MoveNext () [0x00000] in <filename unknown>:0 at Do.Universe.Linux.GNOMESpecialLocationsItemSource.UpdateItems () [0x00000] in <filename unknown>:0 at Do.Universe.Safe.SafeItemSource.UpdateItems () [0x00000] in <filename unknown>:0 . ^[^\Full thread dump: "<unnamed thread>" tid=0x0xb7570700 this=0x0x56f18 thread handle 0x403 state : not waiting owns () at (wrapper managed-to-native) Mono.Unix.Native.Syscall.read (int,intptr,ulong) <0xffffffff> at Mono.Unix.Native.Syscall.read (int,void*,ulong) <0x00023> at Mono.Unix.UnixStream.Read (byte[],int,int) <0x0008b> at NDesk.DBus.Connection.ReadMessage () <0x0003c> at NDesk.DBus.Connection.Iterate () <0x0001b> at NDesk.DBus.BusG/<Init>c__AnonStorey0.<>m__0 (intptr,NDesk.GLib.IOCondition,intptr) <0x00033> at (wrapper native-to-managed) NDesk.DBus.BusG/<Init>c__AnonStorey0.<>m__0 (intptr,NDesk.GLib.IOCondition,intptr) <0xffffffff> at (wrapper managed-to-native) Gtk.Clipboard.gtk_clipboard_wait_is_text_available (intptr) <0xffffffff> at Gtk.Clipboard.WaitIsTextAvailable () <0x00017> at Do.Universe.SelectedTextItem.UpdateSelection (object,System.EventArgs) <0x00027> at Do.Platform.AbstractApplicationService.OnSummoned () <0x00025> at Do.Platform.ApplicationService.<ApplicationService>m__31 (object,System.EventArgs) <0x00013> at Do.Core.Controller.OnSummoned () <0x00025> at Do.Core.Controller.Summon () <0x00027> at Do.Do.Main (string[]) <0x001eb> at (wrapper runtime-invoke) <Module>.runtime_invoke_void_object (object,intptr,intptr,intptr) <0xffffffff> "<unnamed thread>" tid=0x0xb2c81b40 this=0x0x194150 thread handle 0x412 state : interrupted state owns () at (wrapper managed-to-native) System.IO.InotifyWatcher.ReadFromFD (intptr,byte[],intptr) <0xffffffff> at System.IO.InotifyWatcher.Monitor () <0x0005f> at System.Threading.Thread.StartInternal () <0x00057> at (wrapper runtime-invoke) object.runtime_invoke_void__this__ (object,intptr,intptr,intptr) <0xffffffff> "Universe Update Dispatcher" tid=0x0xb29ffb40 this=0x0x569d8 thread handle 0x41b state : interrupted state owns () at (wrapper managed-to-native) System.Threading.WaitHandle.WaitOne_internal (System.Threading.WaitHandle,intptr,int,bool) <0xffffffff> at System.Threading.WaitHandle.WaitOne (System.TimeSpan,bool) <0x00133> at System.Threading.WaitHandle.WaitOne (System.TimeSpan) <0x00022> at Do.Core.UniverseManager.UniverseUpdateLoop () <0x0007a> at System.Threading.Thread.StartInternal () <0x00057> at (wrapper runtime-invoke) object.runtime_invoke_void__this__ (object,intptr,intptr,intptr) <0xffffffff> Tomboy.NotesItemSource "Tomboy Notes" encountered an error in UpdateItems: System.TypeInitializationException: An exception was thrown by the type initializer for Tomboy.TomboyDBus ---> System.Exception: Unable to open the session message bus. ---> System.ArgumentNullException: Argument cannot be null. Parameter name: address at NDesk.DBus.Bus.Open (System.String address) [0x00000] in <filename unknown>:0 at NDesk.DBus.Bus.get_Session () [0x00000] in <filename unknown>:0 --- End of inner exception stack trace --- at NDesk.DBus.Bus.get_Session () [0x00000] in <filename unknown>:0 at Tomboy.TomboyDBus..cctor () [0x00000] in <filename unknown>:0 --- End of inner exception stack trace --- at Tomboy.NotesItemSource.UpdateItems () [0x00000] in <filename unknown>:0 at Do.Universe.Safe.SafeItemSource.UpdateItems () [0x00000] in <filename unknown>:0 . Firefox.PlacesItemSource "Firefox Places" encountered an error in UpdateItems: System.InvalidCastException: Cannot cast from source type to destination type. at Mono.Data.Sqlite.SqliteDataReader.VerifyType (Int32 i, DbType typ) [0x00000] in <filename unknown>:0 at Mono.Data.Sqlite.SqliteDataReader.GetString (Int32 i) [0x00000] in <filename unknown>:0 at Firefox.PlacesItemSource+<LoadPlaceItems>c__Iterator3.MoveNext () [0x00000] in <filename unknown>:0 at System.Collections.Generic.List`1[Firefox.PlaceItem].AddEnumerable (IEnumerable`1 enumerable) [0x00000] in <filename unknown>:0 at System.Collections.Generic.List`1[Firefox.PlaceItem]..ctor (IEnumerable`1 collection) [0x00000] in <filename unknown>:0 at System.Linq.Enumerable.ToArray[PlaceItem] (IEnumerable`1 source) [0x00000] in <filename unknown>:0 at Firefox.PlacesItemSource.UpdateItems () [0x00000] in <filename unknown>:0 at Do.Universe.Safe.SafeItemSource.UpdateItems () [0x00000] in <filename unknown>:0 . Do.Universe.Linux.GNOMESpecialLocationsItemSource "GNOME Special Locations" encountered an error in UpdateItems: System.IO.FileNotFoundException: Could not find file "/root/.gtk-bookmarks". File name: '/root/.gtk-bookmarks' at System.IO.FileStream..ctor (System.String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, Boolean anonymous, FileOptions options) [0x00000] in <filename unknown>:0 at System.IO.FileStream..ctor (System.String path, FileMode mode, FileAccess access, FileShare share) [0x00000] in <filename unknown>:0 at (wrapper remoting-invoke-with-check) System.IO.FileStream:.ctor (string,System.IO.FileMode,System.IO.FileAccess,System.IO.FileShare) at System.IO.File.OpenRead (System.String path) [0x00000] in <filename unknown>:0 at System.IO.StreamReader..ctor (System.String path, System.Text.Encoding encoding, Boolean detectEncodingFromByteOrderMarks, Int32 bufferSize) [0x00000] in <filename unknown>:0 at System.IO.StreamReader..ctor (System.String path) [0x00000] in <filename unknown>:0 at (wrapper remoting-invoke-with-check) System.IO.StreamReader:.ctor (string) at Do.Universe.Linux.GNOMESpecialLocationsItemSource+<ReadBookmarkItems>c__Iterator3.MoveNext () [0x00000] in <filename unknown>:0 at Do.Universe.Linux.GNOMESpecialLocationsItemSource.UpdateItems () [0x00000] in <filename unknown>:0 at Do.Universe.Safe.SafeItemSource.UpdateItems () [0x00000] in <filename unknown>:0 . It stops when I try my key combination, ctrl-alt-. It does not pop up though.

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