<div class='api-docs-breadcrumbs'><a href="../index.html">test</a> / <a href="./foo.html">foo</a></div> <h1>foo</h1> <div class="node-page-main" data-platform="" data-kotlin-version=""><div class="tags"><div class="spacer"></div> <div class="tags__tag kotlin-version"></div> </div> <a name="$foo()"></a> <div class="signature"><code><span class="keyword">fun </span><span class="identifier">foo</span><span class="symbol">(</span><span class="symbol">)</span><span class="symbol">: </span><span class="identifier">Unit</span></code></div> <div class="sample" data-min-compiler-version="1.3"><pre><code class="lang-kotlin"> fun main(args: Array<String>) { //sampleStart val words = listOf("a", "abc", "ab", "def", "abcd") val byLength = words.groupBy { it.length } println(byLength.keys) // [1, 3, 2, 4] println(byLength.values) // [[a], [abc, def], [ab], [abcd]] val mutableByLength: MutableMap<Int, MutableList<String>> = words.groupByTo(mutableMapOf()) { it.length } // same content as in byLength map, but the map is mutable println("mutableByLength == byLength is ${mutableByLength == byLength}") // true //sampleEnd }</code></pre></div> </div>