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Update sorting-by-functions example to use slices.SortFunc

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This commit is contained in:
Eli Bendersky 2023-08-21 12:47:17 -07:00
parent 655a3b6a9e
commit 2166e61181
4 changed files with 109 additions and 92 deletions
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66
examples/sorting-by-functions/sorting-by-functions.go
View File

@ -7,39 +7,47 @@
package main
import (
"cmp"
"fmt"
"sort"
"slices"
)
// In order to sort by a custom function in Go, we need a
// corresponding type. Here we've created a `byLength`
// type that is just an alias for the builtin `[]string`
// type.
type byLength []string
// We implement `sort.Interface` - `Len`, `Less`, and
// `Swap` - on our type so we can use the `sort` package's
// generic `Sort` function. `Len` and `Swap`
// will usually be similar across types and `Less` will
// hold the actual custom sorting logic. In our case we
// want to sort in order of increasing string length, so
// we use `len(s[i])` and `len(s[j])` here.
func (s byLength) Len() int {
return len(s)
}
func (s byLength) Swap(i, j int) {
s[i], s[j] = s[j], s[i]
}
func (s byLength) Less(i, j int) bool {
return len(s[i]) < len(s[j])
}
// With all of this in place, we can now implement our
// custom sort by converting the original `fruits` slice
// to `byLength`, and then use `sort.Sort` on that typed
// slice.
func main() {
fruits := []string{"peach", "banana", "kiwi"}
sort.Sort(byLength(fruits))
// We implement a comparison function for string
// lengths. `cmp.Compare` is helpful for this.
lenCmp := func(a, b string) int {
return cmp.Compare(len(a), len(b))
}
// Now we can call `slices.SortFunc` with this custom
// comparison function to sort `fruits` by name length.
slices.SortFunc(fruits, lenCmp)
fmt.Println(fruits)
// We can use the same technique to sort a slice of
// values that aren't built-in types.
type Person struct {
name string
age int
}
people := []Person{
Person{name: "Jax", age: 37},
Person{name: "TJ", age: 25},
Person{name: "Alex", age: 72},
}
// Sort `people` by age using `slices.SortFunc`.
//
// Note: if the `Person` struct is large,
// you may want the slice to contain `*Person` instead
// and adjust the sorting function accordingly. If in
// doubt, [benchmark](testing-and-benchmarking)!
slices.SortFunc(people,
func(a, b Person) int {
return cmp.Compare(a.age, b.age)
})
fmt.Println(people)
}

4
examples/sorting-by-functions/sorting-by-functions.hash
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@ -1,2 +1,2 @@
e5a6006366e05ee7785eebac8ba588e4b937a197
h4g4vaLBtkw
9902d1c5654b64d8b381ea7888c0793ac8ab4a97
3EaTknAZHMu

9
examples/sorting-by-functions/sorting-by-functions.sh
View File

@ -1,10 +1,3 @@
# Running our program shows a list sorted by string
# length, as desired.
$ go run sorting-by-functions.go
[kiwi peach banana]
# By following this same pattern of creating a custom
# type, implementing the three `Interface` methods on that
# type, and then calling sort.Sort on a collection of that
# custom type, we can sort Go slices by arbitrary
# functions.
[{TJ 25} {Jax 37} {Alex 72}]

122
public/sorting-by-functions generated
View File

@ -45,7 +45,7 @@ in Go.</p>
</td>
<td class="code leading">
<a href="https://go.dev/play/p/h4g4vaLBtkw"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<a href="https://go.dev/play/p/3EaTknAZHMu"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">package</span> <span class="nx">main</span></span></span></code></pre>
</td>
</tr>
@ -57,65 +57,97 @@ in Go.</p>
<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"><span class="kn">import</span> <span class="p">(</span>
</span></span><span class="line"><span class="cl"> <span class="s">&#34;cmp&#34;</span>
</span></span><span class="line"><span class="cl"> <span class="s">&#34;fmt&#34;</span>
</span></span><span class="line"><span class="cl"> <span class="s">&#34;sort&#34;</span>
</span></span><span class="line"><span class="cl"> <span class="s">&#34;slices&#34;</span>
</span></span><span class="line"><span class="cl"><span class="p">)</span></span></span></code></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>In order to sort by a custom function in Go, we need a
corresponding type. Here we&rsquo;ve created a <code>byLength</code>
type that is just an alias for the builtin <code>[]string</code>
type.</p>
</td>
<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"><span class="kd">type</span> <span class="nx">byLength</span> <span class="p">[]</span><span class="kt">string</span></span></span></code></pre>
<pre class="chroma"><code><span class="line"><span class="cl"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <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">&#34;peach&#34;</span><span class="p">,</span> <span class="s">&#34;banana&#34;</span><span class="p">,</span> <span class="s">&#34;kiwi&#34;</span><span class="p">}</span></span></span></code></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>We implement <code>sort.Interface</code> - <code>Len</code>, <code>Less</code>, and
<code>Swap</code> - on our type so we can use the <code>sort</code> package&rsquo;s
generic <code>Sort</code> function. <code>Len</code> and <code>Swap</code>
will usually be similar across types and <code>Less</code> will
hold the actual custom sorting logic. In our case we
want to sort in order of increasing string length, so
we use <code>len(s[i])</code> and <code>len(s[j])</code> here.</p>
<p>We implement a comparison function for string
lengths. <code>cmp.Compare</code> is helpful for this.</p>
</td>
<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"><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="nf">Len</span><span class="p">()</span> <span class="kt">int</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <span class="k">return</span> <span class="nb">len</span><span class="p">(</span><span class="nx">s</span><span class="p">)</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span>
</span></span><span class="line"><span class="cl"><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="nf">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>
</span></span><span class="line"><span class="cl"> <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>
</span></span><span class="line"><span class="cl"><span class="p">}</span>
</span></span><span class="line"><span class="cl"><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="nf">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>
</span></span><span class="line"><span class="cl"> <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">&lt;</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>
</span></span><span class="line"><span class="cl"><span class="p">}</span></span></span></code></pre>
<pre class="chroma"><code><span class="line"><span class="cl"> <span class="nx">lenCmp</span> <span class="o">:=</span> <span class="kd">func</span><span class="p">(</span><span class="nx">a</span><span class="p">,</span> <span class="nx">b</span> <span class="kt">string</span><span class="p">)</span> <span class="kt">int</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <span class="k">return</span> <span class="nx">cmp</span><span class="p">.</span><span class="nf">Compare</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="nx">a</span><span class="p">),</span> <span class="nb">len</span><span class="p">(</span><span class="nx">b</span><span class="p">))</span>
</span></span><span class="line"><span class="cl"> <span class="p">}</span></span></span></code></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>With all of this in place, we can now implement our
custom sort by converting the original <code>fruits</code> slice
to <code>byLength</code>, and then use <code>sort.Sort</code> on that typed
slice.</p>
<p>Now we can call <code>slices.SortFunc</code> with this custom
comparison function to sort <code>fruits</code> by name length.</p>
</td>
<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"> <span class="nx">slices</span><span class="p">.</span><span class="nf">SortFunc</span><span class="p">(</span><span class="nx">fruits</span><span class="p">,</span> <span class="nx">lenCmp</span><span class="p">)</span>
</span></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">fruits</span><span class="p">)</span></span></span></code></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>We can use the same technique to sort a slice of
values that aren&rsquo;t built-in types.</p>
</td>
<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"> <span class="kd">type</span> <span class="nx">Person</span> <span class="kd">struct</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <span class="nx">name</span> <span class="kt">string</span>
</span></span><span class="line"><span class="cl"> <span class="nx">age</span> <span class="kt">int</span>
</span></span><span class="line"><span class="cl"> <span class="p">}</span></span></span></code></pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><code><span class="line"><span class="cl"> <span class="nx">people</span> <span class="o">:=</span> <span class="p">[]</span><span class="nx">Person</span><span class="p">{</span>
</span></span><span class="line"><span class="cl"> <span class="nx">Person</span><span class="p">{</span><span class="nx">name</span><span class="p">:</span> <span class="s">&#34;Jax&#34;</span><span class="p">,</span> <span class="nx">age</span><span class="p">:</span> <span class="mi">37</span><span class="p">},</span>
</span></span><span class="line"><span class="cl"> <span class="nx">Person</span><span class="p">{</span><span class="nx">name</span><span class="p">:</span> <span class="s">&#34;TJ&#34;</span><span class="p">,</span> <span class="nx">age</span><span class="p">:</span> <span class="mi">25</span><span class="p">},</span>
</span></span><span class="line"><span class="cl"> <span class="nx">Person</span><span class="p">{</span><span class="nx">name</span><span class="p">:</span> <span class="s">&#34;Alex&#34;</span><span class="p">,</span> <span class="nx">age</span><span class="p">:</span> <span class="mi">72</span><span class="p">},</span>
</span></span><span class="line"><span class="cl"> <span class="p">}</span></span></span></code></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Sort <code>people</code> by age using <code>slices.SortFunc</code>.</p>
<p>Note: if the <code>Person</code> struct is large,
you may want the slice to contain <code>*Person</code> instead
and adjust the sorting function accordingly. If in
doubt, <a href="testing-and-benchmarking">benchmark</a>!</p>
</td>
<td class="code">
<pre class="chroma"><code><span class="line"><span class="cl"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <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">&#34;peach&#34;</span><span class="p">,</span> <span class="s">&#34;banana&#34;</span><span class="p">,</span> <span class="s">&#34;kiwi&#34;</span><span class="p">}</span>
</span></span><span class="line"><span class="cl"> <span class="nx">sort</span><span class="p">.</span><span class="nf">Sort</span><span class="p">(</span><span class="nf">byLength</span><span class="p">(</span><span class="nx">fruits</span><span class="p">))</span>
</span></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">fruits</span><span class="p">)</span>
<pre class="chroma"><code><span class="line"><span class="cl"> <span class="nx">slices</span><span class="p">.</span><span class="nf">SortFunc</span><span class="p">(</span><span class="nx">people</span><span class="p">,</span>
</span></span><span class="line"><span class="cl"> <span class="kd">func</span><span class="p">(</span><span class="nx">a</span><span class="p">,</span> <span class="nx">b</span> <span class="nx">Person</span><span class="p">)</span> <span class="kt">int</span> <span class="p">{</span>
</span></span><span class="line"><span class="cl"> <span class="k">return</span> <span class="nx">cmp</span><span class="p">.</span><span class="nf">Compare</span><span class="p">(</span><span class="nx">a</span><span class="p">.</span><span class="nx">age</span><span class="p">,</span> <span class="nx">b</span><span class="p">.</span><span class="nx">age</span><span class="p">)</span>
</span></span><span class="line"><span class="cl"> <span class="p">})</span>
</span></span><span class="line"><span class="cl"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">people</span><span class="p">)</span>
</span></span><span class="line"><span class="cl"><span class="p">}</span></span></span></code></pre>
</td>
</tr>
@ -126,29 +158,13 @@ slice.</p>
<tr>
<td class="docs">
<p>Running our program shows a list sorted by string
length, as desired.</p>
</td>
<td class="code leading">
<td class="code">
<pre class="chroma"><code><span class="line"><span class="cl"><span class="gp">$</span> go run sorting-by-functions.go
</span></span><span class="line"><span class="cl"><span class="go">[kiwi peach banana]</span></span></span></code></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>By following this same pattern of creating a custom
type, implementing the three <code>Interface</code> methods on that
type, and then calling sort.Sort on a collection of that
custom type, we can sort Go slices by arbitrary
functions.</p>
</td>
<td class="code empty">
</span></span><span class="line"><span class="cl"><span class="go">[kiwi peach banana]
</span></span></span><span class="line"><span class="cl"><span class="go">[{TJ 25} {Jax 37} {Alex 72}]</span></span></span></code></pre>
</td>
</tr>
@ -167,7 +183,7 @@ functions.</p>
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