379 lines
19 KiB
Plaintext
Generated
379 lines
19 KiB
Plaintext
Generated
<!DOCTYPE html>
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<html>
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<meta charset="utf-8">
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<title>Go by Example: Collection Functions</title>
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<body>
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<div class="example" id="collection-functions">
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<h2><a href="./">Go by Example</a>: Collection Functions</h2>
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<table>
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<tr>
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<td class="docs">
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<p>We often need our programs to perform operations on
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collections of data, like selecting all items that
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satisfy a given predicate or mapping all items to a new
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collection with a custom function.</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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<td class="docs">
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<p>In some languages it’s idiomatic to use <a href="http://en.wikipedia.org/wiki/Generic_programming">generic</a>
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data structures and algorithms. Go does not support
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generics; in Go it’s common to provide collection
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functions if and when they are specifically needed for
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your program and data types.</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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<p>Here are some example collection functions for slices
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of <code>strings</code>. You can use these examples to build your
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own functions. Note that in some cases it may be
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clearest to just inline the collection-manipulating
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code directly, instead of creating and calling a
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helper function.</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/8hI6oPNEfyh"><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">"strings"</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>Index returns the first index of the target string <code>t</code>, or
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-1 if no match is found.</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="nx">Index</span><span class="p">(</span><span class="nx">vs</span> <span class="p">[]</span><span class="kt">string</span><span class="p">,</span> <span class="nx">t</span> <span class="kt">string</span><span class="p">)</span> <span class="kt">int</span> <span class="p">{</span>
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<span class="k">for</span> <span class="nx">i</span><span class="p">,</span> <span class="nx">v</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">vs</span> <span class="p">{</span>
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<span class="k">if</span> <span class="nx">v</span> <span class="o">==</span> <span class="nx">t</span> <span class="p">{</span>
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<span class="k">return</span> <span class="nx">i</span>
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<span class="p">}</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="o">-</span><span class="mi">1</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>Include returns <code>true</code> if the target string t is in the
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slice.</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="nx">Include</span><span class="p">(</span><span class="nx">vs</span> <span class="p">[]</span><span class="kt">string</span><span class="p">,</span> <span class="nx">t</span> <span class="kt">string</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="nx">Index</span><span class="p">(</span><span class="nx">vs</span><span class="p">,</span> <span class="nx">t</span><span class="p">)</span> <span class="o">>=</span> <span class="mi">0</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>Any returns <code>true</code> if one of the strings in the slice
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satisfies the predicate <code>f</code>.</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="nx">Any</span><span class="p">(</span><span class="nx">vs</span> <span class="p">[]</span><span class="kt">string</span><span class="p">,</span> <span class="nx">f</span> <span class="kd">func</span><span class="p">(</span><span class="kt">string</span><span class="p">)</span> <span class="kt">bool</span><span class="p">)</span> <span class="kt">bool</span> <span class="p">{</span>
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<span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">v</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">vs</span> <span class="p">{</span>
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<span class="k">if</span> <span class="nx">f</span><span class="p">(</span><span class="nx">v</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">return</span> <span class="kc">true</span>
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<span class="p">}</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="kc">false</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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<td class="docs">
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<p>All returns <code>true</code> if all of the strings in the slice
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satisfy the predicate <code>f</code>.</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="nx">All</span><span class="p">(</span><span class="nx">vs</span> <span class="p">[]</span><span class="kt">string</span><span class="p">,</span> <span class="nx">f</span> <span class="kd">func</span><span class="p">(</span><span class="kt">string</span><span class="p">)</span> <span class="kt">bool</span><span class="p">)</span> <span class="kt">bool</span> <span class="p">{</span>
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<span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">v</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">vs</span> <span class="p">{</span>
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<span class="k">if</span> <span class="p">!</span><span class="nx">f</span><span class="p">(</span><span class="nx">v</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">return</span> <span class="kc">false</span>
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<span class="p">}</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="kc">true</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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<td class="docs">
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<p>Filter returns a new slice containing all strings in the
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slice that satisfy the predicate <code>f</code>.</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="nx">Filter</span><span class="p">(</span><span class="nx">vs</span> <span class="p">[]</span><span class="kt">string</span><span class="p">,</span> <span class="nx">f</span> <span class="kd">func</span><span class="p">(</span><span class="kt">string</span><span class="p">)</span> <span class="kt">bool</span><span class="p">)</span> <span class="p">[]</span><span class="kt">string</span> <span class="p">{</span>
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<span class="nx">vsf</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">([]</span><span class="kt">string</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span>
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<span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">v</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">vs</span> <span class="p">{</span>
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<span class="k">if</span> <span class="nx">f</span><span class="p">(</span><span class="nx">v</span><span class="p">)</span> <span class="p">{</span>
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<span class="nx">vsf</span> <span class="p">=</span> <span class="nb">append</span><span class="p">(</span><span class="nx">vsf</span><span class="p">,</span> <span class="nx">v</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="nx">vsf</span>
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<span class="p">}</span>
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</pre></div>
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</td>
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<td class="docs">
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<p>Map returns a new slice containing the results of applying
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the function <code>f</code> to each string in the original slice.</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="nx">Map</span><span class="p">(</span><span class="nx">vs</span> <span class="p">[]</span><span class="kt">string</span><span class="p">,</span> <span class="nx">f</span> <span class="kd">func</span><span class="p">(</span><span class="kt">string</span><span class="p">)</span> <span class="kt">string</span><span class="p">)</span> <span class="p">[]</span><span class="kt">string</span> <span class="p">{</span>
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<span class="nx">vsm</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">([]</span><span class="kt">string</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="nx">vs</span><span class="p">))</span>
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<span class="k">for</span> <span class="nx">i</span><span class="p">,</span> <span class="nx">v</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">vs</span> <span class="p">{</span>
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<span class="nx">vsm</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span> <span class="p">=</span> <span class="nx">f</span><span class="p">(</span><span class="nx">v</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="nx">vsm</span>
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<span class="p">}</span>
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</pre></div>
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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="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
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</pre></div>
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</td>
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</tr>
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<td class="docs">
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<p>Here we try out our various collection functions.</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">var</span> <span class="nx">strs</span> <span class="p">=</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">"apple"</span><span class="p">,</span> <span class="s">"pear"</span><span class="p">,</span> <span class="s">"plum"</span><span class="p">}</span>
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</pre></div>
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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="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">Index</span><span class="p">(</span><span class="nx">strs</span><span class="p">,</span> <span class="s">"pear"</span><span class="p">))</span>
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</pre></div>
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</td>
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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="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">Include</span><span class="p">(</span><span class="nx">strs</span><span class="p">,</span> <span class="s">"grape"</span><span class="p">))</span>
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</pre></div>
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</td>
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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="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">Any</span><span class="p">(</span><span class="nx">strs</span><span class="p">,</span> <span class="kd">func</span><span class="p">(</span><span class="nx">v</span> <span class="kt">string</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="nx">strings</span><span class="p">.</span><span class="nx">HasPrefix</span><span class="p">(</span><span class="nx">v</span><span class="p">,</span> <span class="s">"p"</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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<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="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">All</span><span class="p">(</span><span class="nx">strs</span><span class="p">,</span> <span class="kd">func</span><span class="p">(</span><span class="nx">v</span> <span class="kt">string</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="nx">strings</span><span class="p">.</span><span class="nx">HasPrefix</span><span class="p">(</span><span class="nx">v</span><span class="p">,</span> <span class="s">"p"</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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<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="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">Filter</span><span class="p">(</span><span class="nx">strs</span><span class="p">,</span> <span class="kd">func</span><span class="p">(</span><span class="nx">v</span> <span class="kt">string</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="nx">strings</span><span class="p">.</span><span class="nx">Contains</span><span class="p">(</span><span class="nx">v</span><span class="p">,</span> <span class="s">"e"</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>The above examples all used anonymous functions,
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but you can also use named functions of the correct
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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="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">Map</span><span class="p">(</span><span class="nx">strs</span><span class="p">,</span> <span class="nx">strings</span><span class="p">.</span><span class="nx">ToUpper</span><span class="p">))</span>
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</pre></div>
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<td class="docs">
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<td class="code">
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<div class="highlight"><pre><span class="p">}</span>
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</pre></div>
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</td>
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</table>
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<table>
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<td class="code">
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<div class="highlight"><pre><span class="gp">$</span> go run collection-functions.go
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<span class="go">2</span>
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<span class="go">false</span>
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<span class="go">true</span>
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<span class="go">false</span>
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<span class="go">[peach apple pear]</span>
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<span class="go">[PEACH APPLE PEAR PLUM]</span>
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</pre></div>
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</td>
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</table>
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<p class="next">
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Next example: <a href="string-functions">String Functions</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/collection-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('');codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"strings\"\u000A)\u000A');codeLines.push('func Index(vs []string, t string) int {\u000A for i, v := range vs {\u000A if v == t {\u000A return i\u000A }\u000A }\u000A return -1\u000A}\u000A');codeLines.push('func Include(vs []string, t string) bool {\u000A return Index(vs, t) \x3E= 0\u000A}\u000A');codeLines.push('func Any(vs []string, f func(string) bool) bool {\u000A for _, v := range vs {\u000A if f(v) {\u000A return true\u000A }\u000A }\u000A return false\u000A}\u000A');codeLines.push('func All(vs []string, f func(string) bool) bool {\u000A for _, v := range vs {\u000A if !f(v) {\u000A return false\u000A }\u000A }\u000A return true\u000A}\u000A');codeLines.push('func Filter(vs []string, f func(string) bool) []string {\u000A vsf := make([]string, 0)\u000A for _, v := range vs {\u000A if f(v) {\u000A vsf = append(vsf, v)\u000A }\u000A }\u000A return vsf\u000A}\u000A');codeLines.push('func Map(vs []string, f func(string) string) []string {\u000A vsm := make([]string, len(vs))\u000A for i, v := range vs {\u000A vsm[i] = f(v)\u000A }\u000A return vsm\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' var strs = []string{\"peach\", \"apple\", \"pear\", \"plum\"}\u000A');codeLines.push(' fmt.Println(Index(strs, \"pear\"))\u000A');codeLines.push(' fmt.Println(Include(strs, \"grape\"))\u000A');codeLines.push(' fmt.Println(Any(strs, func(v string) bool {\u000A return strings.HasPrefix(v, \"p\")\u000A }))\u000A');codeLines.push(' fmt.Println(All(strs, func(v string) bool {\u000A return strings.HasPrefix(v, \"p\")\u000A }))\u000A');codeLines.push(' fmt.Println(Filter(strs, func(v string) bool {\u000A return strings.Contains(v, \"e\")\u000A }))\u000A');codeLines.push(' fmt.Println(Map(strs, strings.ToUpper))\u000A');codeLines.push('}\u000A');codeLines.push('');
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