9e216da9ef
After go1.16, go will use module mode by default, even when the repository is checked out under GOPATH or in a one-off directory. Add go.mod, go.sum to keep this repo buildable without opting out of the module mode. > go mod init github.com/mmcgrana/gobyexample > go mod tidy > go mod vendor In module mode, the 'vendor' directory is special and its contents will be actively maintained by the go command. pygments aren't the dependency the go will know about, so it will delete the contents from vendor directory. Move it to `third_party` directory now. And, vendor the blackfriday package. Note: the tutorial contents are not affected by the change in go1.16 because all the examples in this tutorial ask users to run the go command with the explicit list of files to be compiled (e.g. `go run hello-world.go` or `go build command-line-arguments.go`). When the source list is provided, the go command does not have to compute the build list and whether it's running in GOPATH mode or module mode becomes irrelevant.
185 lines
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185 lines
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title>Go by Example: Sorting by Functions</title>
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<link rel=stylesheet href="site.css">
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</head>
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<script>
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onkeydown = (e) => {
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if (e.key == "ArrowLeft") {
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window.location.href = 'sorting';
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}
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if (e.key == "ArrowRight") {
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window.location.href = 'panic';
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}
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}
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</script>
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<body>
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<div class="example" id="sorting-by-functions">
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<h2><a href="./">Go by Example</a>: Sorting by Functions</h2>
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<table>
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<tr>
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<td class="docs">
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<p>Sometimes we’ll want to sort a collection by something
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other than its natural order. For example, suppose we
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wanted to sort strings by their length instead of
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alphabetically. Here’s an example of custom sorts
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in Go.</p>
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</td>
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<td class="code empty leading">
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<a href="http://play.golang.org/p/h4g4vaLBtkw"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
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<span class="s">"fmt"</span>
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<span class="s">"sort"</span>
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<span class="p">)</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>In order to sort by a custom function in Go, we need a
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corresponding type. Here we’ve created a <code>byLength</code>
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type that is just an alias for the builtin <code>[]string</code>
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type.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">type</span> <span class="nx">byLength</span> <span class="p">[]</span><span class="kt">string</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>We implement <code>sort.Interface</code> - <code>Len</code>, <code>Less</code>, and
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<code>Swap</code> - on our type so we can use the <code>sort</code> package’s
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generic <code>Sort</code> function. <code>Len</code> and <code>Swap</code>
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will usually be similar across types and <code>Less</code> will
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hold the actual custom sorting logic. In our case we
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want to sort in order of increasing string length, so
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we use <code>len(s[i])</code> and <code>len(s[j])</code> here.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="kd">func</span> <span class="p">(</span><span class="nx">s</span> <span class="nx">byLength</span><span class="p">)</span> <span class="nx">Len</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span>
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<span class="k">return</span> <span class="nb">len</span><span class="p">(</span><span class="nx">s</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="kd">func</span> <span class="p">(</span><span class="nx">s</span> <span class="nx">byLength</span><span class="p">)</span> <span class="nx">Swap</span><span class="p">(</span><span class="nx">i</span><span class="p">,</span> <span class="nx">j</span> <span class="kt">int</span><span class="p">)</span> <span class="p">{</span>
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<span class="nx">s</span><span class="p">[</span><span class="nx">i</span><span class="p">],</span> <span class="nx">s</span><span class="p">[</span><span class="nx">j</span><span class="p">]</span> <span class="p">=</span> <span class="nx">s</span><span class="p">[</span><span class="nx">j</span><span class="p">],</span> <span class="nx">s</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span>
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<span class="p">}</span>
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<span class="kd">func</span> <span class="p">(</span><span class="nx">s</span> <span class="nx">byLength</span><span class="p">)</span> <span class="nx">Less</span><span class="p">(</span><span class="nx">i</span><span class="p">,</span> <span class="nx">j</span> <span class="kt">int</span><span class="p">)</span> <span class="kt">bool</span> <span class="p">{</span>
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<span class="k">return</span> <span class="nb">len</span><span class="p">(</span><span class="nx">s</span><span class="p">[</span><span class="nx">i</span><span class="p">])</span> <span class="p"><</span> <span class="nb">len</span><span class="p">(</span><span class="nx">s</span><span class="p">[</span><span class="nx">j</span><span class="p">])</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>With all of this in place, we can now implement our
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custom sort by converting the original <code>fruits</code> slice
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to <code>byLength</code>, and then use <code>sort.Sort</code> on that typed
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slice.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
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<span class="nx">fruits</span> <span class="o">:=</span> <span class="p">[]</span><span class="kt">string</span><span class="p">{</span><span class="s">"peach"</span><span class="p">,</span> <span class="s">"banana"</span><span class="p">,</span> <span class="s">"kiwi"</span><span class="p">}</span>
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<span class="nx">sort</span><span class="p">.</span><span class="nx">Sort</span><span class="p">(</span><span class="nx">byLength</span><span class="p">(</span><span class="nx">fruits</span><span class="p">))</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">fruits</span><span class="p">)</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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</tr>
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</table>
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<table>
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<tr>
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<td class="docs">
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<p>Running our program shows a list sorted by string
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length, as desired.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="gp">$</span> go run sorting-by-functions.go
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<span class="go">[kiwi peach banana]</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>By following this same pattern of creating a custom
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type, implementing the three <code>Interface</code> methods on that
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type, and then calling sort.Sort on a collection of that
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custom type, we can sort Go slices by arbitrary
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functions.</p>
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</td>
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<td class="code empty">
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</td>
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</tr>
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</table>
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<p class="next">
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Next example: <a href="panic">Panic</a>.
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</p>
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<p class="footer">
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by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/sorting-by-functions">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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</p>
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</div>
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<script>
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var codeLines = [];
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codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"sort\"\u000A)\u000A');codeLines.push('type byLength []string\u000A');codeLines.push('func (s byLength) Len() int {\u000A return len(s)\u000A}\u000Afunc (s byLength) Swap(i, j int) {\u000A s[i], s[j] \u003D s[j], s[i]\u000A}\u000Afunc (s byLength) Less(i, j int) bool {\u000A return len(s[i]) \u003C len(s[j])\u000A}\u000A');codeLines.push('func main() {\u000A fruits :\u003D []string{\"peach\", \"banana\", \"kiwi\"}\u000A sort.Sort(byLength(fruits))\u000A fmt.Println(fruits)\u000A}\u000A');codeLines.push('');codeLines.push('');
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</script>
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<script src="site.js" async></script>
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</body>
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</html>
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