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<div class="example" id="range">
<h2><a href="./">Go by Example</a>: Range</h2>
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<p><em>range</em> iterates over elements in a variety of data
structures. Let&rsquo;s see how to use <code>range</code> with some
of the data structures we&rsquo;ve already learned.</p>
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<a href="http://play.golang.org/p/g9DqcAkPVA"><img title="Run code" src="play.png" class="run" /></a>
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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<div class="highlight"><pre><span class="kn">import</span> <span class="s">&quot;fmt&quot;</span>
</pre></div>
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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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<p>Here we use <code>range</code> to sum the numbers in a slice.
Arrays work like this too.</p>
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<div class="highlight"><pre> <span class="nx">nums</span> <span class="o">:=</span> <span class="p">[]</span><span class="kt">int</span><span class="p">{</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">}</span>
<span class="nx">sum</span> <span class="o">:=</span> <span class="mi">0</span>
<span class="k">for</span> <span class="nx">_</span><span class="p">,</span> <span class="nx">num</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">nums</span> <span class="p">{</span>
<span class="nx">sum</span> <span class="o">+=</span> <span class="nx">num</span>
<span class="p">}</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;sum:&quot;</span><span class="p">,</span> <span class="nx">sum</span><span class="p">)</span>
</pre></div>
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<p><code>range</code> on arrays and slices provides both the
index and value for each entry. Above we didn&rsquo;t
need the index, so we ignored it with the
blank identifier <code>_</code>. Sometimes we actually want
the indexes though.</p>
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<div class="highlight"><pre> <span class="k">for</span> <span class="nx">i</span><span class="p">,</span> <span class="nx">num</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">nums</span> <span class="p">{</span>
<span class="k">if</span> <span class="nx">num</span> <span class="o">==</span> <span class="mi">3</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;index:&quot;</span><span class="p">,</span> <span class="nx">i</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
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<p><code>range</code> on map iterates over key/value pairs.</p>
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<div class="highlight"><pre> <span class="nx">kvs</span> <span class="o">:=</span> <span class="kd">map</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="s">&quot;a&quot;</span><span class="p">:</span> <span class="s">&quot;apple&quot;</span><span class="p">,</span> <span class="s">&quot;b&quot;</span><span class="p">:</span> <span class="s">&quot;banana&quot;</span><span class="p">}</span>
<span class="k">for</span> <span class="nx">k</span><span class="p">,</span> <span class="nx">v</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">kvs</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Printf</span><span class="p">(</span><span class="s">&quot;%s -&gt; %s\n&quot;</span><span class="p">,</span> <span class="nx">k</span><span class="p">,</span> <span class="nx">v</span><span class="p">)</span>
<span class="p">}</span>
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<p><code>range</code> on strings iterates over Unicode code
points. The first value is the starting byte index
of the <code>rune</code> and the second the <code>rune</code> itself.</p>
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<div class="highlight"><pre> <span class="k">for</span> <span class="nx">i</span><span class="p">,</span> <span class="nx">c</span> <span class="o">:=</span> <span class="k">range</span> <span class="s">&quot;go&quot;</span> <span class="p">{</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">i</span><span class="p">,</span> <span class="nx">c</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
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<div class="highlight"><pre><span class="gp">$</span> go run range.go
<span class="go">sum: 9</span>
<span class="go">index: 1</span>
<span class="go">a -&gt; apple</span>
<span class="go">b -&gt; banana</span>
<span class="go">0 103</span>
<span class="go">1 111</span>
</pre></div>
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<p class="next">
Next example: <a href="functions">Functions</a>.
</p>
<p class="footer">
by <a href="https://twitter.com/mmcgrana">@mmcgrana</a> | <a href="mailto:mmcgrana@gmail.com">feedback</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/range">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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