[PHP]array

<span>/*</span><span>
|----------------------------------------------------------
|array_map();将回调函数作用到给定数组的单元上
|array_column();快速实现：将二维数组转为一维数组
|----------------------------------------------------------
</span><span>*/<br></span>

<span>例一：<br>$records</span> = <span>array</span><span>(
    </span><span>array</span><span>(
        </span>'id' => 2135,
        'first_name' => 'John',
        'last_name' => 'Doe',<span>
    )</span>,
    <span>array</span><span>(
        </span>'id' => 3245,
        'first_name' => 'Sally',
        'last_name' => 'Smith',<span>
    )</span>,
    <span>array</span><span>(
        </span>'id' => 5342,
        'first_name' => 'Jane',
        'last_name' => 'Jones',<span>
    )</span>,
    <span>array</span><span>(
        </span>'id' => 5623,
        'first_name' => 'Peter',
        'last_name' => 'Doe',<span>
    )
);
 
</span><span>$first_names</span> = array_column(<span>$records</span>, 'first_name'<span>);
</span><span>print_r</span>(<span>$first_names</span>);<br>/*<br>输出：

Array
(
    [0] => John
    [1] => Sally
    [2] => Jane
    [3] => Peter
)

<span>例二：<br>$last_names</span> = array_column(<span>$records</span>, 'last_name', 'id'<span>);
</span><span>print_r</span>(<span>$last_names</span>);<br>/*<br>输出：

Array
(
    [2135] => Doe
    [3245] => Smith
    [5342] => Jones
    [5623] => Doe
)

<span>当没有array_column()函数情况下，

</span><span>//</span><span>使用array_map()实现例一：</span>
<span>$a</span> = <span>array_map</span>(<span>function</span>(<span>$element</span>){ 　<span>//</span><span>$records作为参数传入回调函数</span>
　　<span>return</span> <span>$element</span>['last_name'];　　 <span>//</span><span>返回数组元素值的last_name对应值</span><span>
}</span>, <span>$records</span>);　　　　　　　　　　　　　 <span>//</span><span>array_map返回数组，相当于把每个$element['last_name']存入新数组，所以是新建的索引</span>

<span>//</span><span>使用foreach实现例一：</span>
<span>foreach</span>(<span>$records</span> <span>as</span> <span>$v</span><span>)
{
    </span><span>$b</span>[] = <span>$v</span>['last_name'<span>];
}</span>

<span>//</span><span>使用foreach实现例二：</span>
<span>$c</span> = <span>array</span><span>();
</span><span>foreach</span>(<span>$records</span> <span>as</span> <span>$k</span>=><span>$v</span><span>)
{
　</span><span>$c</span> += <span>array</span>(<span>$v</span>['id']=><span>$v</span>['last_name']); <span>//</span><span>使用+运算符, 以追加的形式(不改变原数组索引), 合并组装的数组</span><span>
}　　　　　　　　　　　　　　　　　　　　　　   </span><span>//</span><span>若使用array_merge，数字键名将被重新编号</span>