gistfile1.php

<?php
 
function array_partition($array, $callback, $preserveKeys = false) {
    $partitions = array();
    foreach($array as $key => $value) {
        $partitionName = $callback($value, $key);
        if(!array_key_exists($partitionName, $partitions)) {
            $partitions[$partitionName] = array(); 
        }
        if($preserveKeys) {
            $partitions[$partitionName][$key] = $value;
        }
        else {
            $partitions[$partitionName][] = $value;
        }
    }
    return $partitions;
}

$movies = array();
$movies[] = array(
    'title' => 'a',
    'category' => 'foo'
);
$movies[] = array(
    'title' => 'b',
    'category' => 'bar'
);
$movies[] = array(
    'title' => 'c',
    'category' => 'foo'
);
$movies[] = array(
    'title' => 'd',
    'category' => 'bar'
);

var_dump(array_partition($movies, function($movie) {
    return $movie['category'];
}));



array(2) {
  ["foo"]=>
  array(2) {
    [0]=>
    array(2) {
      ["title"]=>
      string(1) "a"
      ["category"]=>
      string(3) "foo"
    }
    [1]=>
    array(2) {
      ["title"]=>
      string(1) "c"
      ["category"]=>
      string(3) "foo"
    }
  }
  ["bar"]=>
  array(2) {
    [0]=>
    array(2) {
      ["title"]=>
      string(1) "b"
      ["category"]=>
      string(3) "bar"
    }
    [1]=>
    array(2) {
      ["title"]=>
      string(1) "d"
      ["category"]=>
      string(3) "bar"
    }
  }
}