如何通过 count_chars 和 array_map 快速处理字符频率？

gitbox 2025-09-17

1. count_chars 函数概述

count_chars 是一个内建函数，用于计算字符串中每个字符出现的频率，并返回一个关联数组。这个数组的键是字符的 ASCII 码，值是该字符在字符串中出现的次数。

示例：

<span><span><span class="hljs-variable">$string</span></span><span> = </span><span><span class="hljs-string">"hello world!"</span></span><span>;
</span><span><span class="hljs-variable">$char_count</span></span><span> = </span><span><span class="hljs-title function_ invoke__">count_chars</span></span><span>(</span><span><span class="hljs-variable">$string</span></span><span>, </span><span><span class="hljs-number">1</span></span><span>);  </span><span><span class="hljs-comment">// 1 参数表示返回频率的数组</span></span><span>

</span><span><span class="hljs-title function_ invoke__">print_r</span></span><span>(</span><span><span class="hljs-variable">$char_count</span></span><span>);
</span></span>

输出结果为：

<span><span><span class="hljs-title function_ invoke__">Array</span></span><span>
(
    [</span><span><span class="hljs-number">104</span></span><span>] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [</span><span><span class="hljs-number">101</span></span><span>] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [</span><span><span class="hljs-number">108</span></span><span>] =&gt; </span><span><span class="hljs-number">2</span></span><span>
    [</span><span><span class="hljs-number">111</span></span><span>] =&gt; </span><span><span class="hljs-number">2</span></span><span>
    [</span><span><span class="hljs-number">119</span></span><span>] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [</span><span><span class="hljs-number">114</span></span><span>] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [</span><span><span class="hljs-number">100</span></span><span>] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [</span><span><span class="hljs-number">33</span></span><span>] =&gt; </span><span><span class="hljs-number">1</span></span><span>
)
</span></span>

在上述示例中，count_chars 返回了字符串中每个字符（按 ASCII 码）的频率。例如，字符 h（ASCII 码 104）出现了 1 次，字符 l（ASCII 码 108）出现了 2 次。

2. 将字符频率转为可读形式

通常，我们希望看到字符的实际值而不是 ASCII 码。为此，我们可以结合 array_map 函数对返回的数组进行处理，将 ASCII 码转换为字符。

array_map 函数接受一个回调函数，并对数组的每个元素应用该回调函数。在我们的场景中，我们可以用它将 ASCII 码转换成对应的字符。

示例：

<span><span><span class="hljs-variable">$string</span></span><span> = </span><span><span class="hljs-string">"hello world!"</span></span><span>;
</span><span><span class="hljs-variable">$char_count</span></span><span> = </span><span><span class="hljs-title function_ invoke__">count_chars</span></span><span>(</span><span><span class="hljs-variable">$string</span></span><span>, </span><span><span class="hljs-number">1</span></span><span>);

</span><span><span class="hljs-comment">// 将 ASCII 码转换为字符</span></span><span>
</span><span><span class="hljs-variable">$char_count</span></span><span> = </span><span><span class="hljs-title function_ invoke__">array_map</span></span><span>(function(</span><span><span class="hljs-variable">$key</span></span><span>) {
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-variable">$key</span></span><span>);  </span><span><span class="hljs-comment">// chr() 函数将 ASCII 码转为字符</span></span><span>
}, </span><span><span class="hljs-title function_ invoke__">array_keys</span></span><span>(</span><span><span class="hljs-variable">$char_count</span></span><span>));

</span><span><span class="hljs-comment">// 将频率与字符关联</span></span><span>
</span><span><span class="hljs-variable">$char_count</span></span><span> = </span><span><span class="hljs-title function_ invoke__">array_combine</span></span><span>(</span><span><span class="hljs-variable">$char_count</span></span><span>, </span><span><span class="hljs-title function_ invoke__">array_values</span></span><span>(</span><span><span class="hljs-variable">$char_count</span></span><span>));

</span><span><span class="hljs-title function_ invoke__">print_r</span></span><span>(</span><span><span class="hljs-variable">$char_count</span></span><span>);
</span></span>

输出结果为：

<span><span><span class="hljs-title function_ invoke__">Array</span></span><span>
(
    [h] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [e] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [l] =&gt; </span><span><span class="hljs-number">2</span></span><span>
    [o] =&gt; </span><span><span class="hljs-number">2</span></span><span>
    [w] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [r] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [d] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [!] =&gt; </span><span><span class="hljs-number">1</span></span><span>
)
</span></span>

此时我们就可以看到字符及其频率了，输出中每个字符的频率也清晰可见。

3. 综合使用 count_chars 和 array_map 计算字符频率

通过上述两步，我们可以快速计算出字符频率并将其转化为人类可读的格式。可以把这两个步骤封装成一个函数，简化重复操作。

函数示例：

<span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">getCharFrequency</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-variable">$string</span></span></span><span>) {
    </span><span><span class="hljs-variable">$char_count</span></span><span> = </span><span><span class="hljs-title function_ invoke__">count_chars</span></span><span>(</span><span><span class="hljs-variable">$string</span></span><span>, </span><span><span class="hljs-number">1</span></span><span>);
    </span><span><span class="hljs-variable">$char_count</span></span><span> = </span><span><span class="hljs-title function_ invoke__">array_map</span></span><span>(function(</span><span><span class="hljs-variable">$key</span></span><span>) {
        </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">chr</span></span><span>(</span><span><span class="hljs-variable">$key</span></span><span>);  
    }, </span><span><span class="hljs-title function_ invoke__">array_keys</span></span><span>(</span><span><span class="hljs-variable">$char_count</span></span><span>));
    
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-title function_ invoke__">array_combine</span></span><span>(</span><span><span class="hljs-variable">$char_count</span></span><span>, </span><span><span class="hljs-title function_ invoke__">array_values</span></span><span>(</span><span><span class="hljs-variable">$char_count</span></span><span>));
}

</span><span><span class="hljs-variable">$string</span></span><span> = </span><span><span class="hljs-string">"hello world!"</span></span><span>;
</span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-title function_ invoke__">getCharFrequency</span></span><span>(</span><span><span class="hljs-variable">$string</span></span><span>);

</span><span><span class="hljs-title function_ invoke__">print_r</span></span><span>(</span><span><span class="hljs-variable">$result</span></span><span>);
</span></span>

输出结果为：

<span><span><span class="hljs-title function_ invoke__">Array</span></span><span>
(
    [h] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [e] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [l] =&gt; </span><span><span class="hljs-number">2</span></span><span>
    [o] =&gt; </span><span><span class="hljs-number">2</span></span><span>
    [w] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [r] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [d] =&gt; </span><span><span class="hljs-number">1</span></span><span>
    [!] =&gt; </span><span><span class="hljs-number">1</span></span><span>
)
</span></span>

通过 getCharFrequency 函数，我们可以快速得到任何字符串的字符频率统计。无论字符串的长度如何，count_chars 和 array_map 都能提供高效的解决方案。

4. 小结

在 PHP 中，利用 count_chars 和 array_map 函数，我们可以快速且高效地处理字符频率。count_chars 提供了一个原始的频率统计，而 array_map 则能帮助我们将结果转换为更直观的格式。通过结合这两个函数，你可以在字符串分析、文本处理等场景中节省大量时间和精力。

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