linq-to-objects

问题 I have a double[][] that I want to convert to a CSV string format (i.e. each row in a line, and row elements separated by commas). I wrote it like this: public static string ToCSV(double[][] array) { return String.Join(Environment.NewLine, Array.ConvertAll(array, row => String.Join(",", Array.ConvertAll(row, x => x.ToString()))); } Is there a more elegant way to write this using LINQ? (I know, one could use temporary variables to make this look better, but this code format better conveys what

问题 I have 2 instances of a class that implements the IEnumerable interface. I would like to create a new object and combine both of them into one. I understand I can use the for..each to do this. Is there a linq/lambda expression way of doing this? EDIT public class Messages : IEnumerable, IEnumerable<Message> { private List<Message> message = new List<Message>(); //Other methods } Code to combine MessagesCombined messagesCombined = new MessagesCombined(); MessagesFirst messagesFirst =

问题 What's a good LINQ equivalent of this pesudo-code: "given a list of strings, for each string that doesn't contain a tab character, concatenate it (with a pipe delimiter) to the end of the previous string, and return the resulting sequence" ? More Info: I have a List<string> representing lines in a tab-delimited text file. The last field in each line is always a multiline text field, and the file was generated by a buggy system that mishandles fields with embedded newlines. So I end up with a

问题 LINQ drives me crazy. Why does following query not return the duplicates, whereas it works with only one identifier? Where is my error? ' generate some test-data ' Dim source As New DataTable source.Columns.Add(New DataColumn("RowNumber", GetType(Int32))) source.Columns.Add(New DataColumn("Value1", GetType(Int32))) source.Columns.Add(New DataColumn("Value2", GetType(Int32))) source.Columns.Add(New DataColumn("Text", GetType(String))) Dim rnd As New Random() For i As Int32 = 1 To 100 Dim

问题 LINQ to Objects supports queries on string objects but when I use code such as below: string SomeText = "this is some text in a string"; return SomeText.Take(6).ToString(); All I get is: System.Linq.Enumerable+<TakeIterator>d__3a`1[System.Char] This is discussed as an "accident" in this question but this is what I am actually trying to do and I cannot find it through search anywhere. I know there are other ways to manipulate strings but then I also know you can do some really cool tricks with

问题 I currently have a list that contains the following CountryCode (string) CountryStr (string) RegionStr (string) RegionID (int) AreaStr (string) AreaID (int) This is a flattened set of linked data (so basically the results of a joined search that ive stored) The MVC route will only pass one string which I then need to match up to the data at the right level in the heirachy. So I'm trying to query the CountryStr then if it doesn't produce results the region then the area; but I need to do that

问题 This question already has answers here : Preserving order with LINQ (6 answers) Closed 6 years ago . var source = new List<string> { "A1", "A2", "B1", "B2" }; var filtered = source.Where(s => s.StartsWith("A")); foreach (var s in filtered) Console.WriteLine(s); // outputs first A1 and then A2 It seems like Enumerable.Where keeps the original order of elements when used on an ordered IEnumerable (such as a List<T> or T[] ). Is this always the case? If yes, where is this documented? 回答1:

问题 i have written below query in LINQ to perform left join but its throwing error: var qry = from c in dc.category_feature_Name_trans_SelectAll_Active() join p in dc.product_category_feature_trans_SelectAll() on c.cft_id equals p.cft_id into cp from p in cp.DefaultIfEmpty() select new { c.cft_id, c.feature_id, c.feature_name, p.product_id , p.value }; Error: Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web

问题 I'm getting the following error when trying to use an async lambda within IEnumerable.SelectMany : var result = myEnumerable.SelectMany(async (c) => await Functions.GetDataAsync(c.Id)); The type arguments for method 'IEnumerable System.Linq.Enumerable.SelectMany(this IEnumerable, Func>)' cannot be inferred from the usage. Try specifying the type arguments explicitly Where GetDataAsync is defined as: public interface IFunctions { Task<IEnumerable<DataItem>> GetDataAsync(string itemId); }

问题 I have a linq to objects query in a recursive loop and afraid when the objects approach more then 1000 and a have more then 100 users on the site -- my website will break. so is it possible to compile a linq to objects query. The linq query does nothing more then find the direct children of a node. 回答1: To see why the concept of compilation doesn't really make sense for LINQ to Object queries, it's useful to understand how LINQ is implemented. First, it should be clear that LINQ queries