array_filter(): Filtering Arrays

<?php
 //Syntax
 array_filter(array $array,
              ?callable $callback = null, 
              int $mode = 0): array

The array_filter() function returns the filtered array and accepts three parameters:

1. $array – an input array
2. $callback– (optional) a function, if not supplied, all empty entries of the array will be removed.
3. $mode – (optional) by default pass value as the only argument to the callback.
   Use the ARRAY_FILTER_USE_KEY flag to pass key instead.
   Use the ARRAY_FILTER_USE_BOTH flag to pass both value and key.

Remove empty array elements

PHP considers a value empty when converting to boolean type returns false. The following values are considered empty:

1. FALSE
2. 0, '0', "0", 0.0, or -0.0
3. Empty string '' and ""
4. Empty array (array with zero elements) array() or []
5. NULL or undefined variables

When you use the array_filter function without a callback function it removes all the values which PHP considered as empty:

Example: Remove all empty values with array_filter()

<?php
 $a = [1,2, 0,'0',0.0,false,null,'',[],4,5,"" ];
 $b = array_filter($a); 
 print_r($b);
/* Prints: 
Array
(
    [0] => 1
    [1] => 2
    [9] => 4
    [10] => 5
)*/

Example: Remove empty strings from an array with array_filter()

<?php
 $a = ['a', '  ', null, 'b',  "  ", 'c', 0, false];
 $b = array_filter($a, 'filter_empty_strings');

 function filter_empty_strings($v){
  if (is_string($v)){
   return '' !== trim($v);
  }
  return true;
 }

 var_dump($b);
/* prints: 
array(6) {
  [0]=> string(1) "a"
  [2]=> NULL
  [3]=> string(1) "b"
  [5]=> string(1) "c"
  [6]=> int(0)
  [7]=> bool(false)
}*/

Example: Validate a list of email addresses with array_filter()

<?php
 function validateEmailAddress($v) {
  return filter_var($v, FILTER_VALIDATE_EMAIL);
 }
 $list = [
    'admin@brainbell.com',
    'admin@brainbell_com',
    'info[at]brainbell.com',
    'info@brainbell.com'
    ];
 $validList = array_filter($list, 'validateEmailAddress');
 print_r($validList);
 
 /*Prints:
Array
(
    [0] => admin@brainbell.com
    [3] => info@brainbell.com
)*/

The array_filter() filter out the invalid addresses so that only (syntactically) valid email addresses are left. As you would expect, the code just prints out the two valid email addresses.

Note: The array_filter() function keeps the keys/values association intact. If you need to reindex the array after removing the empty elements, use: array_values() function.

<?php
 /*follow previous example code*/
 $validList = array_values(
               array_filter($list, 'validateEmailAddress')
              );
 print_r($validList);
/*Prints:
Array
(
    [0] => admin@brainbell.com
    [1] => info@brainbell.com
)*/

Filter arrays by indexed key

Use the ARRAY_FILTER_USE_KEY flag if you want to deal with array indexes instead of the values.

<?php
 function filterKey($v) {
  return $v !== 1;
 }
 $a = ['a','b','c'];
 $f = array_filter($a, 'filterKey', 
                   ARRAY_FILTER_USE_KEY );
 
 print_r($f);
 /*
Array
(
    [0] => a
    [2] => c
)*/

Filter arrays by keys and values

Use the ARRAY_FILTER_USE_BOTH flag if you want to deal with both values and keys.

<?php
 function filterBoth($value, $key) {
  return !($key === 1 && $value === 'b');
 }

 $a = ['a','b','c'];
 $f = array_filter($a, 'filterBoth', 
                   ARRAY_FILTER_USE_BOTH );
 
 print_r($f);
 /*
Array
(
    [0] => a
    [2] => c
)*/

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Working with arrays: