对象数组的索引数组

问题描述：

How do I create (in PHP) and array of an array of objects? For example, say I have:

$arr[0] = array("eref_id" => "A001", "eref_child" => "A100", "level" => 1);
$arr[1] = array("eref_id" => "A002", "eref_child" => "A200", "level" => 2);
$arr[2] = array("eref_id" => "A003", "eref_child" => "A300", "level" => 3);
$arr[3] = array("eref_id" => "A003", "eref_child" => "A310", "level" => 3);

An I want a new array where the elements of "arr" are the "eref_id" and "eref_child" but the index to the array is the "level" element. So basically,

$newarr[1] would contain $arr[0]
$newarr[2] would contain $arr[1]
$newarr[3] would contain $arr[2]

and $arr[3] (since both have a "level" of 3).

This would contain an array of $arr[2] and $arr[3].

Hopefully this makes sense

如何创建（在PHP中）和对象数组的数组？例如，假设我有： p>

  $ arr [0] = array（“eref_id”=＆gt;“A001”，“eref_child”=＆gt;“A100”，“  level“=＆gt; 1）; 
 $ arr [1] = array（”eref_id“=＆gt;”A002“，”eref_child“=＆gt;”A200“，”level“=＆gt; 2）; 
 $  arr [2] = array（“eref_id”=＆gt;“A003”，“eref_child”=＆gt;“A300”，“level”=＆gt; 3）; 
 $ arr [3] = array（“eref_id”=  ＆gt;“A003”，“eref_child”=＆gt;“A310”，“level”=＆gt; 3）; 
  code>  pre> 
 
 我想要一个新的数组，其中 “arr”的元素是“eref_id”和“eref_child”，但数组的索引是“level”元素。 所以基本上， p> 
 
 
  $ newarr [1]将包含$ arr [0] 
 $ newarr [2]将包含$ arr [1] 
 $ newarr [3] 将包含$ arr [2] 
  code>  pre> 
 
 和 $ arr [3]  code>（因为两者的“级别”均为3）。   p> 
 
 
这将包含 $ arr [2]  code>和 $ arr [3]  code>的数组。 p> 
 \  n 
希望这是有道理的 p> 
  div>

答

<?php
$arr[0] = array("eref_id" => "A001", "eref_child" => "A100", "level" => 1);
$arr[1] = array("eref_id" => "A002", "eref_child" => "A200", "level" => 2);
$arr[2] = array("eref_id" => "A003", "eref_child" => "A300", "level" => 3);
$arr[3] = array("eref_id" => "A003", "eref_child" => "A310", "level" => 3);

foreach($arr as $a){
    $newarr[$a['level']][] = $a;
}

echo '<pre>',print_r($newarr),'</pre>';

答

You can do it easily with ouzo goodies

In php 5.4:

$result = Arrays::toMap($arr, Functions::extract()['level']);

In php 5.3:

$result = Arrays::toMap($arr, function($elem) { return $elem['level']; });

If you had an array of e.g. User objects:

$cities = Arrays::map($users, Functions::extract()->getAddress('home')->city);

Check out: http://ouzo.readthedocs.org/en/latest/utils/functions.html#extract

对象数组的索引数组

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