PHP array_filter: How to Filter an Array in PHP

The array_filter() function filters the array’s values using the callback function. The array_filter() function passes each value of an input array to the callback function. If the callback function returns a true value, the current value from ant input is returned into the result array.

PHP array_filter

The array_filter() is a built-in PHP function that filters the values of an array using a callback function. The array_filter() method iterates over each value in an array, passing them to the callback function. If the callback function returns a true value, the current value from an array is returned to the result array. Array keys are preserved. Array keys are preserved.

How to filter array in PHP

To filter an array in PHP, use the array_filter() method. The array_filter() takes an array and filter function and returns the filtered array. The filter function is a custom user-defined function with its logic and based on that, it filters out the array values and returns them.

Let’s take an example.

<?php

// app.php

function even($value)
{
  return $value % 2 == 0;
}

$arr = [1, 2, 3, 4, 5];
print_r(array_filter($arr,"even"));

In the above code, we are checking every array item that is even; if it is odd, it will be filtered out from the array, and only even item stays in the array.

The output is following.

We can also write the array_filter() function like the following.

<?php

// app.php

$arr = [1, 2, 3, 4, 5];
$output = array_filter($arr, function($value) {
  return $value % 2 == 0;  
});
print_r($output);

The output will be the same as above; we have just written an anonymous function.

<?php

// app.php

$arr = ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4];
$outputA = array_filter($arr, function($k) {
  return $k == 'b';
}, ARRAY_FILTER_USE_KEY);
print_r($outputA);

ARRAY_FILTER_USE_BOTH

<?php

// app.php

$arr = ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4];

$outputB = array_filter($arr, function($v, $k) {
  return $k == 'b' || $v == 4;
}, ARRAY_FILTER_USE_BOTH);
print_r($outputB);

Accessing Keys in array_filter() function

<?php

// app.php

$data = array('first' => 1, 'second' => 2, 'third' => 3);
$data = array_filter($data, function ($item) use (&$data) {
    echo "Filtering key ", key($data)."\n";
    next($data);
});

That’s it for this example.