multi-sort of associative array in PHP

Question

Consider the following associative array

$arr = Array
(        
    [banana] => 2
    [cherry] => 1
    [orange] => 3
    [grapefruit] => 1
    [apple] => 1
)

I want to sort it in a way that would be similar to the PLSQL term: A DESC, B ASC (where A is the value and B is the key) meaning:

$arr = Array
(
    [orange] => 3
    [banana] => 2
    [apple] => 1
    [cherry] => 1
    [grapefruit] => 1        
)

so that orange and banana are first because of the VALUE, but then I have apple, cherry and grapefruit in alphabetical order because they have the same VALUE.

What I tried:
1. to run ksort() and then asort()/rsort() hoping that the second sort will bump up orange and banana to the beginning of the array without messing up the alphabetical sort of the other 3 items. I was wrong. it does messes everything up. So I checked out:
2. sort functions and array_multisort(). But apparently it sorts several arrays at once, or a multi-dimensional array.
3. I also tried to define the following compare function:

function cmp($a, $b)
{
    foreach ($a as $key1 => $val1) {
        foreach ($b as $key2 => $val2) {
            if($val1 == $val2){
                return strcmp($key1,$key2);
            }
            else if ($val1 > $val2){
                return 1;
            }
            else{ // $val1 < $val2
                return -1;
            }
        }
    }    
}

and call it with usort() but it also didn't work.

So my question is: is there a PHP method that implements the requested behavior?

For Eugen:
I tried it and it doesn't work before sorting:

Array
(
    [lamb] => 3
    [rule] => 1
    [children] => 1
    [teacher] => 2
    [eager] => 1
)

and after sorting:

Array
(
    [children] => 1
    [eager] => 1
    [rule] => 1
    [teacher] => 2
    [lamb] => 3
)

@Galen in a very sophisticated and powerful way that was never seen on earth ;) — Nir Alfasi
– Nir Alfasi, Commented Jun 16, 2012 at 9:07
Regarding your first approach, it didn't work because PHP sorting is not stable (i.e. maintains order on equal values). — Sarke
– Sarke, Commented Jun 16, 2012 at 9:47

Zbigniew · Accepted Answer · 2012-06-16 09:01:56Z

13

You can use array_multisort

<?php
    $arr = Array
    (        
        'banana' => 2,
        'cherry' => 1,
        'orange' => 3,
        'grapefruit' => 1,
        'apple' => 1
    );

    $values = array_values($arr);
    $keys = array_keys($arr);

    //first sort by values desc, then sort by keys asc
    array_multisort($values, SORT_DESC, $keys, SORT_ASC, $arr);

    print_r($arr);
    // output:
    /*
    Array
    (
        [orange] => 3
        [banana] => 2
        [apple] => 1
        [cherry] => 1
        [grapefruit] => 1
    )
    */

?>

It works like this:

for each column used to sort (values and keys for you), create new 1d array with its contents
pass those 1d arrays to array_multisort function in your sorting order (so $values first, then $keys), add sort order for each array
the last argument has to be the array which you want to sort

(Perhaps you will find this explanation easier to understand)

answered Jun 16, 2012 at 9:01

Zbigniew

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3 Comments

Nir Alfasi Over a year ago

I don't know why you got -1, you got +1 from me as your solution indeed works, thanks!!!

Zbigniew Over a year ago

@alfasin thanks :), people're so fast in downvoting and don't event explain why...

Paris Char Over a year ago

If we want to add multiple Sorting flags for each element we want to sort by, will it work?

Eugen Rieck · Accepted Answer · 2012-06-16 09:36:56Z

3

function polysortcmp($a, $b) {
  if ($a[1]<$b[1]) return 1;
  if ($a[1]>$b[1]) return -1;
  if ($a[0]<$b[0]) return -1;
  if ($a[0]>$b[0]) return 1;
  return 0;
}


function polysort(&$arr) {
  foreach ($arr as $k=>$v) $arr[$k]=array($k,$v);
  uasort($arr, "polysortcmp");
  foreach ($arr as $k=>$v) $arr[$k]=$v[1];
}

edited Jun 16, 2012 at 9:36

answered Jun 16, 2012 at 8:53

Eugen Rieck

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4 Comments

Nir Alfasi Over a year ago

it doesn't work. I update the question to show you what is the result if I try it your way.

Eugen Rieck Over a year ago

Sorry, misread you: I sorted by key first, then value - updated my answer.

Nir Alfasi Over a year ago

Now it sorts alphabetically, but the VALUES are in ASC order instead of DESC. I updated my question to show you the current output of your code. You can take the example I gave and run it.

Eugen Rieck Over a year ago

OK, third time is a charm, again updated my answer. For your information: the sort order is in polysortcmp() with $a[1] being the value and $a[0] being the key.

Vaishu · Accepted Answer · 2012-06-16 10:04:43Z

0

array sorting function arsort used..

$arr = array(        
        'banana' => 2,
        'cherry' => 1,
        'orange' => 3,
        'grapefruit' => 1,
        'apple' => 1
    );

arsort($arr);
print_r($arr);

Output

Array ( [orange] => 3 [banana] => 2 [apple] => 1 [grapefruit] => 1 [cherry] => 1 )

answered Jun 16, 2012 at 10:04

Vaishu

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1 Comment

Nir Alfasi Over a year ago

I tried arsort() and it doesn't work. it might work on that specific example I gave - but it will not work on general case.

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