Build associative array based on values of another associative array

Question

I'm looking for an elegant way to turn this array:

Array (
  [foo] => 1
  [bar] => 1
  [zim] => 3
  [dib] => 6
  [gir] => 1
  [gaz] => 3
)

Into this array:

Array (
  [1] => Array ( foo, bar, gir ),
  [3] => Array ( zim, gaz ),
  [6] => Array ( dib )
)

Note:, there is no relationship between the keys or values. They are completely arbitrary and used as examples only. The resulting array should be an associative array grouped by the values of the input array.

Thanks!

hsz · Accepted Answer · 2010-04-21 18:28:57Z

12

$input = array(
  'foo' => 1,
  'bar' => 1,
  'zim' => 3,
  'dib' => 6,
  'gir' => 1,
  'gaz' => 3
)

$output = array();
foreach ( $input as $k => $v ) {
  if ( !isset($output[$v]) ) {
    $output[$v] = array();
  }

  $output[$v][] = $k;
}

answered Apr 21, 2010 at 18:28

hsz

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Comments

animuson · Accepted Answer · 2010-04-21 18:30:24Z

3

I think this will do it just fine:

foreach ($arr1 as $k => $val) $arr2[$val][] = $k;

where $arr1 is the original array outputting the new array to $arr2.

answered Apr 21, 2010 at 18:30

animuson♦

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5 Comments

maček Over a year ago

I thought this would've generated a PHP warning, but nope! Concise and sweet FTW!

maček Over a year ago

@stereofrog, can you detail the "bug"?

maček Over a year ago

@stereofrog, I suppose that's a fair argument. You're right, too. I shouldn't sacrifice reliable functionality just for the sake of trimming a line or two out.

Gutzofter Over a year ago

@stereofrog: I could have sworn I've seen this type of example in the manual pages. Cause if what your saying is true my code is totally fed up.

animuson Over a year ago

I never define variables first, what a waste of a line of code. That's why I use PHP, because you don't have too.

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