How can I check and delete duplicate arrays? - php

Question

how can I check and delete duplicate arrays?
Example:
$a = array(
array(
'id' => 1,
'name' => 'test'
),
// Next array is equal to first, then delete
array(
'id' => 1,
'name' => 'test'
),
// Different array, then continue here
array(
'id' => 2,
'name' => 'other'
)
);
If the array is the same, then delete the duplicate and get only one array.

Answer 1

You can use a lookup table storing serialized arrays. If an array already exists in the lookup table, you have a duplicate and can splice out the key:
$a = array(
array(
'id' => 1,
'name' => 'test'
),
array(
'id' => 1,
'name' => 'test'
),
array(
'id' => 2,
'name' => 'other'
)
);
$seen = [];
for ($i = count($a) - 1; $i >= 0; $i--) {
if (array_key_exists(json_encode($a[$i]), $seen)) {
array_splice($a, $i, 1);
}
else {
$seen[json_encode($a[$i])] = 1;
}
}
print_r($a);
Output:
Array
(
[0] => Array
(
[id] => 1
[name] => test
)
[1] => Array
(
[id] => 2
[name] => other
)
)
Try it!

Answer 2

array_unique()
Example:
$array = array(1, 2, 2, 3);
$array = array_unique($array); // Array is now (1, 2, 3)

Answer 3

You can loop through the parent array, serialize each child array and save it in a third array, and as you are looping, check for the existence of the serial of each next child array to all previous ones saved in the third array. If it exists, remove the current duplicate from the parent array by key. The function below demonstrates this.
function remove_duplicate_nested_arrays($parent_array)
$temporary_array = array(); // declare third, temporary array.
foreach($parent_array as $key => $child_array){ // loop through parent array
$child_array_serial = serialize($child_array); // serialize child each array
if(in_array($child_array_serial,$temporary_array)){ // check if child array serial exists in third array
unset($parent_array[$key]); // unset the child array by key from parent array if it's serial exists in third array
continue;
}
$temporary_array[] = $child_array_serial; // if this point is reached, the serial of child array is not in third array, so add it so duplicates can be detected in future iterations.
}
return $parent_array;
}
This can also be achieved in 1 line, using #Jose Carlos Gp suggestion as follows:
$b = array_map('unserialize', array_unique(array_map('serialize', $a)));
The function above kind of expands on what is actually happening in the 1 liner solution.