Recipe 4.23 Removing Duplicate Elements from an Array
4.23.1 Problem
You want to
eliminate duplicates from an array.
4.23.2 Solution
If the array is already complete, use array_unique(
),
which returns a new array that contains no duplicate values:
$unique = array_unique($array);
If you create the array while processing results, here is a technique
for
numerical arrays:
foreach ($_REQUEST['fruits'] as $fruit) {
if (!in_array($array, $fruit)) { $array[ ] = $fruit; }
}
Here's one for associative arrays:
foreach ($_REQUEST['fruits'] as $fruit) {
$array[$fruit] = $fruit;
}
4.23.3 Discussion
Once processing is completed, array_unique(
)
is the best way to eliminate duplicates. But, if
you're inside a loop, you can eliminate the
duplicate entries from appearing by checking if
they're already in the array.
An even faster method than using in_array(
)
is to create a hybrid array in which the key and the value for each
element are the same. This eliminates the linear check of
in_array( ) but still allows you to take advantage
of the array family of functions that operate over the values of an
array instead of the keys.
In fact, it's faster to use the associative array
method and then call array_values(
)
on the result (or, for that matter, array_keys(
),
but array_values( ) is slightly faster) than to
create a numeric array directly with the overhead of
in_array( ).
4.23.4 See Also
Documentation on array_unique( ) at
http://www.php.net/array-unique.
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