Changing Array Size (PHP Cookbook)

4.7.1. Problem

You want to modify the size of an array, either by making it larger or smaller than its current size.

4.7.2. Solution

Use array_pad( ) to make an array grow:

// start at three
$array = array('apple', 'banana', 'coconut');

// grow to five
$array = array_pad($array, 5, '');

Now, count($array) is 5, and the last two elements contain the empty string.

To reduce an array, you can use array_splice( ):

// no assignment to $array
array_splice($array, 2);

This removes all but the first two elements from $array.

4.7.3. Discussion

Arrays aren't a predeclared size in PHP, so you can resize them on the fly.

To pad an array, use array_pad( ). The first argument is the array to be padded. The next argument is the size and direction you want to pad. To pad to the right, use a positive integer; to pad to the left, use a negative one. The third argument is the value to be assigned to the newly created entries. The function returns a modified array and doesn't alter the original.

Here are some examples:

// make a four-element array with 'dates' to the right
$array = array('apple', 'banana', 'coconut');
$array = array_pad($array, 4, 'dates');
print_r($array);
Array
(
    [0] => apple
    [1] => banana
    [2] => coconut
    [3] => dates
)

// make a six-element array with 'zucchinis' to the left
$array = array_pad($array, -6, 'zucchini');
print_r($array);
Array
(
    [0] => zucchini
    [1] => zucchini
    [2] => apple
    [3] => banana
    [4] => coconut
    [5] => dates
)

Be careful. array_pad($array, 4, 'dates') makes sure an $array is at least four elements long, it doesn't add four new elements. In this case, if $array was already four elements or larger, array_pad( ) would return an unaltered $array.

Also, if you declare a value for a fourth element, $array[4]:

$array = array('apple', 'banana', 'coconut');
$array[4] = 'dates';

you end up with a four-element array with indexes 0, 1, 2, and 4:

Array
(
    [0] => apple
    [1] => banana
    [2] => coconut
    [4] => dates
)

PHP essentially turns this into an associative array that happens to have integer keys.

The array_splice( ) function, unlike array_pad( ), has the side-effect of modifying the original array. It returns the spliced out array. That's why you don't assign the return value to $array. However, like array_pad( ), you can splice from either the right or left. So, calling array_splice( ) with a value of -2 chops off the last two elements from the end:

// make a four-element array
$array = array('apple', 'banana', 'coconut', 'dates');

// shrink to three elements
array_splice($array, 3);

// remove last element, equivalent to array_pop( )
array_splice($array, -1);

// only remaining fruits are apple and banana
print_r($array);
Array
(
    [0] => apple
    [1] => banana
)

4.7. Changing Array Size

4.7.1. Problem

4.7.2. Solution

4.7.3. Discussion

4.7.4. See Also


4.6. Deleting Elements from an Array		4.8. Appending One Array to Another