php - Comparing elements in a multidimensional array

Question

Say i have a multidimensional array. For example:

 Array ( 
         [0] => Array ( 
             [animal_id] => 5494 
             [animal_name] => "Suzy"
             [animal_type] => "zebra" 
             [animal_location] => 0 
             [animal_awake] => 1
             [animal_age] => 3 ) 
         [1] => Array ( 
             [animal_id] => 5494 
             [animal_name] => "Joshua"
             [animal_type] => "panda"
             [animal_location] => 5
             [animal_awake] => 0
             [animal_age] => 8 )
        [2] => Array ( 
             [animal_id] => 5494 
             [animal_name] => "Debra"
             [animal_type] => "snake" 
             [animal_location] => 7 
             [animal_awake] => 1
             [animal_age] => 3 ) 
        [3] => Array ( 
             [animal_id] => 5495 
             [animal_name] => "Caleb"
             [animal_type] =>  "zebra"
             [animal_location] => 0
             [animal_awake] => 1
             [animal_age] => 3 ) 
        [4] => Array ( 
             [animal_id] => 5495 
             [animal_name] => "Joshua"
             [animal_type] =>  "panda"
             [animal_location] => 5 
             [animal_awake] => 0
             [animal_age] => 8 )    
        [5] => Array ( 
             [animal_id] => 5495 
             [animal_name] => "Debra"
             [animal_type] =>  "snake"
             [animal_location] => 7 
             [animal_awake] => 1
             [animal_age] => 3 ) 
        [6] => Array ( 
             [animal_id] => 5496 
             [animal_name] => "Emily"
             [animal_type] =>  "zebra"
             [animal_location] => 0
             [animal_awake] => 1
             [animal_age] => 3 ) 
        [7] => Array ( 
             [animal_id] => 5496 
             [animal_name] => "Joshua"
             [animal_type] =>  "panda"
             [animal_location] => 5 
             [animal_awake] => 0
             [animal_age] => 8 )    
        [8] => Array ( 
             [animal_id] => 5496 
             [animal_name] => "Debra"
             [animal_type] =>  "snake"
             [animal_location] => 7 
             [animal_awake] => 1
             [animal_age] => 3 )             
         )

And i want to compare all the snakes against the snakes, and all the panda's against the panda's etc (but not a snake against a panda) and put the unique elements into an array(all unique elements into a single array), how would i go about doing this. Since they are elements within an array, i'm a bit stumped. Also, i won't know in advance how many different types there will be. For instance, one time i could be passed an multidimensional array with Panda, Bear, Snake -- Next time i could be passed an array with Bird, Cat, Panda, Zebra.

Any ideas?

FINAL OUTPUT

      Array ( 
     [0] => Array ( 
         [animal_id] => 5494 
         [animal_name] => "Suzy"
         [animal_type] => "zebra" 
         [animal_location] => 0 
         [animal_awake] => 1
         [animal_age] => 3 ) 
     [1] => Array ( 
         [animal_id] => 5494 
         [animal_name] => "Joshua"
         [animal_type] => "panda"
         [animal_location] => 5
         [animal_awake] => 0
         [animal_age] => 8 )
    [2] => Array ( 
         [animal_id] => 5495 
         [animal_name] => "Caleb"
         [animal_type] =>  "zebra"
         [animal_location] => 0
         [animal_awake] => 1
         [animal_age] => 3 )    
    [3] => Array ( 
         [animal_id] => 5495 
         [animal_name] => "Debra"
         [animal_type] =>  "snake"
         [animal_location] => 7 
         [animal_awake] => 1
         [animal_age] => 3 ) 
    [4] => Array ( 
         [animal_id] => 5496 
         [animal_name] => "Emily"
         [animal_type] =>  "zebra"
         [animal_location] => 0
         [animal_awake] => 1
         [animal_age] => 3 )    

     )

Answer 1

Array keys must be unique, so lets use that to our advantage.

function get_animal_key($animal) {
    return $animal['animal_type'] . '-' . $animal['animal_name'];
}

$uniques = array();
foreach ($array as $animal) {
    $key = get_animal_key($animal);
    $uniques[$key] = $animal;
}

var_export($uniques);

Gives the following array

array (
  'zebra-Suzy' => 
  array (
    'animal_id' => 5494,
    'animal_name' => 'Suzy',
    'animal_type' => 'zebra',
    'animal_location' => 0,
    'animal_awake' => 1,
    'animal_age' => 3,
  ),
  'panda-Joshua' => 
  array (
    'animal_id' => 5496,
    'animal_name' => 'Joshua',
    'animal_type' => 'panda',
    'animal_location' => 5,
    'animal_awake' => 0,
    'animal_age' => 8,
  ),
  'snake-Debra' => 
  array (
    'animal_id' => 5496,
    'animal_name' => 'Debra',
    'animal_type' => 'snake',
    'animal_location' => 7,
    'animal_awake' => 1,
    'animal_age' => 3,
  ),
  'zebra-Caleb' => 
  array (
    'animal_id' => 5495,
    'animal_name' => 'Caleb',
    'animal_type' => 'zebra',
    'animal_location' => 0,
    'animal_awake' => 1,
    'animal_age' => 3,
  ),
  'zebra-Emily' => 
  array (
    'animal_id' => 5496,
    'animal_name' => 'Emily',
    'animal_type' => 'zebra',
    'animal_location' => 0,
    'animal_awake' => 1,
    'animal_age' => 3,
  ),
)

As you can see, this takes the animal's type and name as the unique identifiers. Your question did not state what makes an animal unique, so alter the above to suit your needs.