Sort a 2d array by a column and obey a dynamic direction variable

Question

I have an array and i want to sort it by value of key [min] (0.2, 0.86 ...) in a desc order. Here is an array:

Array
(
    [0] => Array
        (
            [p1_first_res_avalue] => 0.72413793103448
            [p1_rating_lang_avalue] => 0.2
            [p1_ps_res_avalue] => 0.79310344827586      
            [pid] => 0
            [p1_discipline_e_avalue] => 0.77777777777778
            [p1_rating_lang] => 46
            [p1_first_res] => 59
            [p1_ps_res] => 57
            [p1_discipline_e] => 86
            [min] => 0.2
        )

    [1] => Array
        (
            [p1_discipline_e] => 81
            [p1_first_res] => 55
            [p1_rating_lang] => 38
            [p1_ps_res] => 48
            [p1_discipline_e_avalue] => 1
            [pid] => 1
            [p1_first_res_avalue] => 0.86206896551724
            [p1_rating_lang_avalue] => 1
            [p1_ps_res_avalue] => 1
            [min] => 0.86
        )

   [2] => Array
        (
            [p1_discipline_e] => 81
            [p1_first_res] => 55
            [p1_rating_lang] => 38
            [p1_ps_res] => 48
            [p1_discipline_e_avalue] => 1
            [pid] => 1
            [p1_first_res_avalue] => 0.86206896551724
            [p1_rating_lang_avalue] => 1
            [p1_ps_res_avalue] => 1
            [min] => 0.3
        )
...
)

I've tried to use uasort function, but I can't get access to [min] value of array to compare it. That's what i try ($res is an array, need to sort):

$sortd = 'down';
$f = function($a, $b) use ($sortd) {
        if (($sortd) == 'down') {
            if ($a['min'] == $b['min']) return 0;
            return ($a['min'] > $b['min']) ? -1 : 1;
        }
        else {

        }
    };

foreach ($res as $k => $v) {
    uasort($res[$k], $f);
}

Please, any ideas how to solve the problem?

Duplicate of almost every result for stackoverflow.com/search?q=php+sort+array … — C3roe
– C3roe, Commented Jun 12, 2015 at 22:59

rjdown · Accepted Answer · 2015-06-12 22:55:24Z

2

Your problem seems to be that you're trying to apply the sorting function to each element of the array individually, instead of the array as a whole.

Instead of

foreach ($res as $k => $v) {
    uasort($res[$k], $f);
}

Try just

uasort($res, $f);

answered Jun 12, 2015 at 22:55

rjdown

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Comments

Alex Offshore · Accepted Answer · 2019-03-12 16:51:02Z

Well... I bet nobody expects ~~the Spanish Inquisition~~ that's there is a built-in solution which is about 25 times faster. Please, forget about sorting 2d arrays with u*sort, it worths nothing to just read the manual!

http://php.net/manual/en/function.array-multisort.php

For given case, it's just:

array_multisort(array_column($res, 'min'), SORT_DESC, SORT_NUMERIC, $res);

Even more, it can sort by several columns at once, much like ORDER BY, e.g.:

// ORDER BY `name` ASC, `price` DESC:
array_multisort(
    array_column($rows, 'name'), SORT_ASC,
    array_column($rows, 'price'), SORT_DESC, SORT_NUMERIC,
    $rows
);

Two things you should be aware of: array_column skips rows without requested key, but this is not a problem for data fetched from SELECT or something like that (note that null values are not omitted) and array_multisort doesn't preserve numeric keys. However, both things can be easily worked around without any significant overhead.

Simple benchmark for curious: https://gist.github.com/offshore/fb836c1204da85fe2f34557d970350f9

twentylemon · Accepted Answer · 2015-06-12 22:53:46Z

0

Why wouldn't uasort work? Your comparator would just be

$f = function($a1, $a2) { return $a1['min'] < $a2['min'] ? -1 : 1; };
uasort($res, $f);

You're sorting each subarray - there's no min in thoses values, so there would all be 0. Your function returns 0 when that is the case, so the sort would do nothing.

answered Jun 12, 2015 at 22:53

twentylemon

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Comments

user2182349 · Accepted Answer · 2015-06-13 02:43:06Z

0

uasort may incur significant overhead.

If you want to sort an array of arrays, you can create a flattened version and use asort.

$flat = array();
foreach ($arr as $index => $item) {
    $flat[$index] = $item[$k];
}
asort($flat);

If you want to check the performance, you can use microtime.

answered Jun 13, 2015 at 2:43

user2182349

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