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[PHP]array

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--------------------------------------------------------------------------------------------------------- /* |----------------------------------------------------------|array_map();将回调函数作用到给定数组的单元上|array_column();快速实现:

---------------------------------------------------------------------------------------------------------

<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>

array array_column ( array $input , mixed $column_key [, mixed $index_key ] );

返回input数组中值为column_key的列; 如果指定了可选参数index_key,返回的数组中 对应键 为input数组值index_key对应的值。

 

<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>

 

在取出的多条数据中,典型的二维数组,如果需要使用数据中单一的 值与值 对应的情况,array_column()即可完成,但是面对较复杂的数组结构,foreach才能让你更灵活,不过优先使用系统函数总是首选的。

 

Link: http://www.cnblogs.com/farwish/p/3855831.html

@黑眼诗人 

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