There are a huge amount of functions to deal with arrays in PHP, but I will be going through just a few of the most useful or interesting ones. If you would like me to add a function or two to this list, just tell me and I'll do my best.

In this article we will be using a two arrays:

<?php

$colours_ary = array('blue', 'red', 'orange', 'green');
$database_ary = array(
    'username'  => 'test_username',
    'database'  => 'test_database',
    'password'  => 'test_password',
    'rand_text' => 'Lorem ipsum sit amet',
);

Outputting arrays

There are two functions to outputs arrays, print_r and var_dump. The first just outputs the array, while var_dump displays a lot more information such as data types:

<?php

print_r($database_ary);
var_dump($database_ary);

That would output:

Array
(
    [username] => test_username
    [database] => test_database
    [password] => test_password
    [rand_text] => Lorem ipsum sit amet
)
array(4) {
  ["username"]=>
  string(13) "test_username"
  ["database"]=>
  string(13) "test_database"
  ["password"]=>
  string(13) "test_password"
  ["rand_text"]=>
  string(20) "Lorem ipsum sit amet"
}

foreach

foreach is easily the most used function to deal with arrays. It cycles through the array, and for every item in the array it executes some specified code.

foreach ($colours_ary as $value)
    statement
foreach ($database_ary as $key => $value)
    statement

So for example:

<?php

foreach ($colours_ary as $colour) {
    $db->query('INSERT INTO table VALUES ("' . $colour . '")');
}

Or:

<?php

echo '<ul id="database">';

foreach ($database_ary as $key => $value) {
    echo '<li id="' . $key . '">' . $value . '</li>';
}

echo '</ul>';

is_array

is_array is an extremely simple function - it simply returns whether the function is an array or not. It can be used like this:

<?php

echo is_array($possibly_an_array) ? 'Array' : 'Not an Array';

if (is_array($colours_ary)) {
    foreach ($colours_ary as $value) {
        echo $value . ', ';
    }
} else {
    echo $colours_ary;
}

That code could be shortened, but I wanted to include two examples of how is_array can be used.

array_values

While this function seems a bit pointless at first, I have used it on a couple occasions where not using it would have caused an error. It removes the keys from the array and replaces them with numbers.

<?php

print_r(array_values($database_ary));

That will output:

Array
(
    [0] => test_username
    [1] => test_database
    [2] => test_password
    [3] => Lorem ipsum sit amet
)

array_keys

array_keys is the opposite of array_values, it returns all the keys as an array:

<?php

print_r(array_keys($database_ary));

That will return:

Array
(
    [0] => username
    [1] => database
    [2] => password
    [3] => rand_text
)

array_merge

array_merge is an incredibly useful function that merges two or more arrays together:

<?php

$new_array = array_merge($colours_ary, $database_ary);
print_r($new_array);

That will return:

Array
(
    [0] => blue
    [1] => red
    [2] => orange
    [3] => green
    [username] => test_username
    [database] => test_database
    [password] => test_password
    [rand_text] => Lorem ipsum sit amet
)

asort

asort is short for array sort. It alphabetically orders the array by the values.

<?php

asort($colours_ary);
print_r($colours_ary);

That will return:

Array
(
    [0] => blue
    [3] => green
    [2] => orange
    [1] => red
)

You can also use arsort - array reverse sort. It will sort the array in reverse order.

array_flip

array_flip switches the keys and the values of an array - the keys become the values, and the values become the keys. I'm assuming you don't need an example - it's pretty obvious :)

You can also use this function to remove null elements from an array (thanks to h3x on php.net for this):

<?php
$ar = array(null,'1','2',null,'3',null);
print_r($ar);
/*
result:
Array
(
    [0] => 
    [1] => 1
    [2] => 2
    [3] => 
    [4] => 3
    [5] => 
)
*/

print_r(array_flip(array_flip($ar)));
/*
result:
Array
(
    [1] => 1
    [2] => 2
    [4] => 3
)
*/
?>

array_reverse

array_reverse simply returns the array backwards.

<?php

print_r(array_reverse($database_ary));

That will return:

Array
(
    [rand_text] => Lorem ipsum sit amet
    [password] => test_password
    [database] => test_database
    [username] => test_username
)

implode / explode

implode and explode are functions that turn arrays into strings and back. I will cover implode first. implode turns an array into a string, like this:

<?php

echo implode(', ', $colours_ary);

That will return blue, red, orange, green. explode does the opposite, and turns a string into an array:

<?php

$string = 'value0, value1, etc, value3';
$array = explode(', ', $string);
print_r($array);

That will return:

Array
(
    [0] => value0
    [1] => value1
    [2] => etc
    [3] => value3
)