按值降序对关联数组进行排序，并在值相同时保留顺序

Question

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. eg

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

The result which I want is :

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

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.

Answer 1

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. Group the array by value:

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

   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'] ]; 

2. sort the groups in descending order by key:

    krsort($groups); 

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

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

Answer 2

You can use array_multisort . The function can be a bit confusing, and really hard to explain, but it orders multiple arrays, and the first array provided gets sorted based on the order of subsequent arrays.

Try:

array_multisort($l, SORT_DESC, array_keys($l));

See the example here: https://3v4l.org/oV8Od

It sorts the array by values descending, then is updated by the sort on the keys of the array.