array_map，array_walk和array_filter之间的区别 [英] Difference between array_map, array_walk and array_filter

问题描述

array_map，array_walk和array_filter之间的区别到底是什么?我从文档中可以看到，您可以传递一个回调函数来对提供的数组执行操作.但是我似乎没有发现它们之间有什么特别的区别.

What exactly is the the difference between array_map, array_walk and array_filter. What I could see from documentation is that you could pass a callback function to perform an action on the supplied array. But I don't seem to find any particular difference between them.

他们执行相同的事情吗?
它们可以互换使用吗?

Do they perform the same thing?
Can they be used interchangeably?

如果这些示例有所不同，请提供示例帮助，谢谢您.

I would appreciate your help with illustrative example if they are different at all.

推荐答案

• 更改值:
  • array_map 不能更改输入数组中的值，而 array_map 永远不要更改其参数.
  • Changing Values:
    • array_map cannot change the values inside input array(s) while array_walk can; in particular, array_map never changes its arguments.
    • array_map 无法使用数组键
    • array_map 返回一个新数组， array_walk .
    • array_map returns a new array, array_walk only returns true. Hence, if you don't want to create an array as a result of traversing one array, you should use array_walk.
    • array_map 也可以接收任意数量的数组，并且可以并行遍历它们，而<一个href ="http://php.net/array_walk" rel ="noreferrer"> array_walk 只能在一个上运行.
    • array_walk 可以接收一个额外的任意参数以传递给回调.自PHP 5.3(引入匿名函数以来)，这基本上无关紧要. /li>
    • array_walk can receive an extra arbitrary parameter to pass to the callback. This mostly irrelevant since PHP 5.3 (when anonymous functions were introduced).
    • 所得的array_map数组的长度与最大输入数组的长度相同； array_walk不返回数组，但同时不能更改原始数组的元素数； array_filter 根据过滤功能仅选择数组元素的子集.它确实保留了密钥.
    • The resulting array of array_map has the same length as that of the largest input array; array_walk does not return an array but at the same time it cannot alter the number of elements of original array; array_filter picks only a subset of the elements of the array according to a filtering function. It does preserve the keys.

    示例:

    <pre>
    <?php
    
    $origarray1 = array(2.4, 2.6, 3.5);
    $origarray2 = array(2.4, 2.6, 3.5);
    
    print_r(array_map('floor', $origarray1)); // $origarray1 stays the same
    
    // changes $origarray2
    array_walk($origarray2, function (&$v, $k) { $v = floor($v); }); 
    print_r($origarray2);
    
    // this is a more proper use of array_walk
    array_walk($origarray1, function ($v, $k) { echo "$k => $v", "\n"; });
    
    // array_map accepts several arrays
    print_r(
        array_map(function ($a, $b) { return $a * $b; }, $origarray1, $origarray2)
    );
    
    // select only elements that are > 2.5
    print_r(
        array_filter($origarray1, function ($a) { return $a > 2.5; })
    );
    
    ?>
    </pre>
    

    结果:

    Array
    (
        [0] => 2
        [1] => 2
        [2] => 3
    )
    Array
    (
        [0] => 2
        [1] => 2
        [2] => 3
    )
    0 => 2.4
    1 => 2.6
    2 => 3.5
    Array
    (
        [0] => 4.8
        [1] => 5.2
        [2] => 10.5
    )
    Array
    (
        [1] => 2.6
        [2] => 3.5
    )
    

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