按值对关联数组进行降序排序，并在值相同时保留顺序 [英] Sort an associative array by value in descending and preserve order when values are same

问题描述

我想对一个关联数组进行排序，并且有一个内置函数来实现相同的效果. arsort()，但是此函数的问题在于，当值相同时，它不会保持原始键顺序.例如

I want to sort an associative array and there is an inbuilt function to achieve the same viz. arsort(), but the problem with this function is that it doesn't maintain the original key order when values are same. e.g.

$l = [
    'a' => 1,
    'b' => 2,
    'c' => 2,
    'd' => 4,
    'e' => 5,
    'f' => 5
];

我想要的结果是:

$l = [
    'e' => 5,
    'f' => 5,
    'd' => 4,
    'b' => 2,
    'c' => 2,
    'a' => 1
];

arsort()以降序给出结果，但是当值相同时，它将随机排列元素.这个问题不是 PHP数组多重排序-按值的重复项然后按密钥?.在这个问题中，它要求按字母顺序对相同的数值进行排序，但是在我的问题中，我要的是如果值相同，则按照原始顺序对值进行排序.

arsort() gives the result in descending order but it randomly arranges the element when values are same. This question is not a duplicate of PHP array multiple sort - by value then by key?. In that question it is asking for same numeric value to be sorted alphabetically but in my question I am asking values to sorted according to the original order if they are same.

推荐答案

可能有更有效的方法，但是我认为这应该可以在相同值的组中保持原始键顺序.我将从这个数组开始，例如:

There is probably a more efficient way to do this, but I think this should work to maintain the original key order within groups of the same value. I'll start with this array for example:

$l = [ 'a' => 1, 'b' => 2, 'c' => 2, 'd' => 4, 'g' => 5, 'e' => 5, 'f' => 5 ]; 

1. 按值对数组进行分组:

1. Group the array by value:

foreach ($l as $k => $v) {
    $groups[$v][] = $k;
}

由于 foreach 循环顺序读取数组，因此将以正确的顺序将键插入其各自的组中，这将产生:

Because the foreach loop reads the array sequentially, the keys will be inserted in their respective groups in the correct order, and this will yield:

[1 => ['a'], 2 => ['b', 'c'], 4 => ['d'], 5 => ['g', 'e', 'f'] ];

按键以降序对组进行排序:

sort the groups in descending order by key:

krsort($groups);

使用嵌套循环从分组数组中重新组合排序后的数组:

Reassemble the sorted array from the grouped array with a nested loop:

foreach ($groups as $value => $group) {
    foreach ($group as $key) {
        $sorted[$key] = $value;
    }
}

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