{"id":2401,"date":"2023-06-23T09:25:32","date_gmt":"2023-06-23T02:25:32","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=2401"},"modified":"2023-06-23T09:27:00","modified_gmt":"2023-06-23T02:27:00","slug":"linq-selectmany","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-linq\/linq-selectmany\/","title":{"rendered":"LINQ SelectMany"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you will learn how to use the LINQ <code>SelectMany()<\/code> method to transform items of a sequence into a single flatted sequence.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Introduction to the LINQ SelectMany() method<\/h2>\n\n\n\n<p>The <code>SelectMany()<\/code> method takes a sequence of items, performs a transformation on each item, and generates a new sequence of items for each input item. Finally, it combines all the generated immediate sequences into a single flattened sequence.<\/p>\n\n\n\n<p>Here&#8217;s the syntax of the <code>SelectMany()<\/code> method:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">public<\/span> IEnumerable&lt;TResult&gt; SelectMany&lt;TSource,TResult&gt; (\n    <span class=\"hljs-keyword\">this<\/span> IEnumerable&lt;TSource&gt; source, \n    Func&lt;TSource,IEnumerable&lt;TResult&gt;&gt; selector\n);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>In this syntax:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><code>source <\/code>&#8211; is the sequence of items with type <code><a href=\"https:\/\/csharptutorial.net\/csharp-linq\/csharp-ienumerable\/\">IEnumerable&lt;TSource><\/a><\/code> to transform.<\/li>\n\n\n\n<li><code>selector <\/code>&#8211; is a transformation function that applies to each element of the source sequence.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">LINQ SelectMany() method<\/h2>\n\n\n\n<p>Let&#8217;s take some examples of using the <code>SelectMany()<\/code> method.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">1) Using the LINQ SelectMany() method to flatten a list of arrays of integers<\/h3>\n\n\n\n<p>The following example uses the <code>SelectMany()<\/code> method to flatten a list of an array of integers and return a <code>IEnumerable&lt;int><\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">using<\/span> <span class=\"hljs-keyword\">static<\/span> System.Console;\n\n\n<span class=\"hljs-keyword\">var<\/span> numbers = <span class=\"hljs-keyword\">new<\/span> List&lt;<span class=\"hljs-keyword\">int<\/span>&#91;]&gt;()\n{\n    <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-keyword\">int<\/span>&#91;] { <span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">2<\/span> },\n    <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-keyword\">int<\/span>&#91;] { <span class=\"hljs-number\">3<\/span>, <span class=\"hljs-number\">4<\/span>, <span class=\"hljs-number\">5<\/span>,},\n    <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-keyword\">int<\/span>&#91;] { <span class=\"hljs-number\">6<\/span>, <span class=\"hljs-number\">7<\/span>, <span class=\"hljs-number\">8<\/span>}\n};\n\n\n<span class=\"hljs-keyword\">var<\/span> results = numbers.SelectMany(x =&gt; x);\n<span class=\"hljs-keyword\">foreach<\/span> (<span class=\"hljs-keyword\">var<\/span> number <span class=\"hljs-keyword\">in<\/span> results)\n{\n    WriteLine(number);\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Objects<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-number\">1<\/span>\n<span class=\"hljs-number\">2<\/span>\n<span class=\"hljs-number\">3<\/span>\n<span class=\"hljs-number\">4<\/span>\n<span class=\"hljs-number\">5<\/span>\n<span class=\"hljs-number\">6<\/span>\n<span class=\"hljs-number\">7<\/span>\n<span class=\"hljs-number\">8<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h3 class=\"wp-block-heading\">2) Using the LINQ SelectMany() method to flatten a list of arrays of strings<\/h3>\n\n\n\n<p>Suppose you have an <code>Employee<\/code> class with two properties <code>Name<\/code> and <code>Skills<\/code>. The <code>Skills<\/code> property is a list of strings that represent employees&#8217; skills.<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title\">Employee<\/span>\n{\n    <span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-keyword\">string<\/span> Name { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>;}\n    <span class=\"hljs-keyword\">public<\/span> List&lt;<span class=\"hljs-keyword\">string<\/span>&gt; Skills { <span class=\"hljs-keyword\">get<\/span>; <span class=\"hljs-keyword\">set<\/span>;}\n\n    <span class=\"hljs-function\"><span class=\"hljs-keyword\">public<\/span> <span class=\"hljs-title\">Employee<\/span>(<span class=\"hljs-params\"><span class=\"hljs-keyword\">string<\/span> name, List&lt;<span class=\"hljs-keyword\">string<\/span>&gt; skills<\/span>)<\/span>\n    {\n        Name = name;\n        Skills = skills;\n    }\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The following program uses the <code>SelectMany()<\/code> to get all skills of all employees from a list:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\"><span class=\"hljs-keyword\">using<\/span> <span class=\"hljs-keyword\">static<\/span> System.Console;\n\n<span class=\"hljs-keyword\">var<\/span> employees = <span class=\"hljs-keyword\">new<\/span> List&lt;Employee&gt;()\n{\n    <span class=\"hljs-keyword\">new<\/span> Employee\n    (\n        name: <span class=\"hljs-string\">\"John Doe\"<\/span>,\n        skills: <span class=\"hljs-keyword\">new<\/span> List&lt;<span class=\"hljs-keyword\">string<\/span>&gt; {<span class=\"hljs-string\">\"C#\"<\/span>,<span class=\"hljs-string\">\"ASP.NET Core\"<\/span>,<span class=\"hljs-string\">\"Rest API\"<\/span>}\n    ),\n    <span class=\"hljs-keyword\">new<\/span> Employee\n    (\n        name: <span class=\"hljs-string\">\"Jane Doe\"<\/span>,\n        skills: <span class=\"hljs-keyword\">new<\/span> List&lt;<span class=\"hljs-keyword\">string<\/span>&gt; {<span class=\"hljs-string\">\"Python\"<\/span>,<span class=\"hljs-string\">\"Django\"<\/span>,<span class=\"hljs-string\">\"Fast API\"<\/span>}\n    ),\n\n    <span class=\"hljs-keyword\">new<\/span> Employee\n    (\n        name: <span class=\"hljs-string\">\"Alice Miller\"<\/span>,\n        skills: <span class=\"hljs-keyword\">new<\/span> List&lt;<span class=\"hljs-keyword\">string<\/span>&gt; {<span class=\"hljs-string\">\"JavaScript\"<\/span>,<span class=\"hljs-string\">\"Node.js\"<\/span>,<span class=\"hljs-string\">\"Express\"<\/span>}\n    ),\n};\n\n<span class=\"hljs-keyword\">var<\/span> skills = employees.SelectMany(e =&gt; e.Skills);\n\n<span class=\"hljs-keyword\">foreach<\/span> (<span class=\"hljs-keyword\">var<\/span> skill <span class=\"hljs-keyword\">in<\/span> skills)\n{\n    WriteLine(skill);\n}<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"C#\" data-shcb-language-slug=\"cs\"><span><code class=\"hljs language-cs\">C<span class=\"hljs-meta\">#<\/span>\nASP.NET Core\nRest API\nPython\nDjango\nFast API\nJavaScript\nNode.js\nExpress<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">C#<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">cs<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\">Summary<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use the LINQ <code>SelectMany()<\/code> method to create a single flattened sequence by transforming items of another sequence.<\/li>\n<\/ul>\n<div class=\"helpful-block-content\" data-title=\"\">\n\t<header>\n\t\t<div class=\"wth-question\">Was this tutorial helpful ?<\/div>\n\t\t<div 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