Sort rows of a 2d array by a column of values with negative values first, then sort by absolute values descending - PHP

Matin
April 11, 2023
264 views
0 votes
2 Answers

I have an array like this:

[
    ['array-5', 0],
    ['array-4', 0],
    ['array-1',-1],
    ['array-3', 2],
    ['array-2', 3]
]

I want to sort this in PHP so that negative numbers are ordered before positive numbers, and if the sign is the same, the magnitude (more negative or more positive) has precedence.

For the example above, the desired output would be:

[
    ['array-1',-1],
    ['array-2', 3],
    ['array-3', 2],
    ['array-4', 0],
    ['array-5', 0]
]

Answers

- trincot
- April 11, 2023 at 4:48 pm
- 0 votes
0
If $data has your input, you can call usort like this:
```
usort($data, function ($a, $b) {
    $res = ($b[1] < 0) - ($a[1] < 0);
    $diff = abs($b[1]) - abs($a[1]);
    return $res ? $res : ($diff > 0) - ($diff < 0);
});
```
After this has executed, $data will have the desired order.
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- mickmackusa
- April 12, 2023 at 2:18 am
- 0 votes
0
Sort by negatives first, then sort by absolute value descending.

Code: (Demo)
```
usort(
    $array,
    fn($a, $b) => [$b[1] < 0, abs($b[1])]
                  <=>
                  [$a[1] < 0, abs($a[1])]
);
```
Or separate the abs() calls as a second/fallback evaluation: (Demo)
```
usort(
    $array,
    fn($a, $b) => ($b[1] < 0 <=> $a[1] < 0)
                  ?: (abs($b[1]) <=> abs($a[1]))
);
```
Perhaps more efficient but less concise would be to isolate absolute values by calling abs() on each value only once.

Code: (Demo)
```
$notNegs = [];
$absVals = [];
foreach ($array as [1 => $v]) {
    $abs = abs($v);
    $absVals[] = $abs;
    $notNegs[] = $v === $abs;
}
array_multisort($notNegs, $absVals, SORT_DESC, $array);
```
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