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Array Functions in PHP

Arrays are an important and widely used type in PHP. They are essentially ordered maps that allow developers quick access to key-value storage in their applications. For some basic array examples, see my previous post of working with arrays in PHP.

PHP has over 75 array functions to help you manipulate and use arrays more efficiently. Since that’s a bit overwhelming, I’m just going to go over a few of the more common ones.

1. array_diff

If you have two arrays and you want to find values that are in the first, but not the second, array_diff is probably your best bet. It will compare two or more arrays and return all the values in the first array that are not in the other arrays.

Code

$array1 = ['red', 'blue', 'green'];
$array2 = ['red', 'brown', 'green'];
print_r(array_diff($array1, $array2));

Output

Array
(
    [1] => blue
)

Note: You can similarly compare array keys with array_diff_key.

2. array_filter

When you want to remove certain values from an array array_filter is usually a good option. It allows you to pass a callback function that filters items from an array.

Code

$array = [1, 100, 102, 103];
// Filters out array values < 100
$filteredArray = array_filter($array, function ($value) {
    return $value >= 100;
});
print_r($filteredArray);

Output

Array
(
    [1] => 100
    [2] => 102
    [3] => 103
)

Note: You can also filter using keys with array_filter. Be sure to check out the official documentation for more detailed examples.

3. array_intersect

If you need to know which values are contained in all of two or more arrays you can use array_intersect.

Code

$array1 = ['red', 'blue', 'green'];
$array2 = ['red', 'brown', 'green'];
print_r(array_intersect($array1, $array2));

Output

Array
(
    [0] => red
    [2] => green
)

Note: array_intersect ignores the keys in your compared arrays, but array_intersect_assoc does not.

4. array_keys

Sometimes you just need keys from your array, and array_keys can be very useful for this. It also provides an optional second parameter to search the array values and only return keys of matched elements.

Code

$array = ['a' => 'red', 'b' => 'blue', 'c' => 'green'];
print_r(array_keys($array));
print_r(array_keys($array, 'blue'));

Output

Array
(
    [0] => a
    [1] => b
    [2] => c
)
Array
(
    [0] => b
)

Note: by default the search_value parameter uses a loose comparison, but you can include a third parameter to enforce strict matches.

5. array_map

This is one of my favorite array functions. It allows you to loop over an array and manipulate each value or call some external function. It can be used as a more concise looping method.

Code

$array = ['a' => 'red', 'b' => 'blue', 'c' => 'green'];

$array = array_map(function ($value) {
    return $value . " modified";
}, $array);

print_r($array);

Output

Array
(
    [a] => red modified
    [b] => blue modified
    [c] => green modified
)

Note: You can pass multiple arrays into array_map and use each array as a value in the callback function. For more detailed examples check the documentation.

6. array_merge

If you have two arrays and would like to merge them into a single array, array_merge makes it a snap.

Code

$array1 = ['red', 'blue', 'green'];
$array2 = ['red', 'brown', 'green'];
print_r(array_merge($array1, $array2));

Output

Array
(
    [0] => red
    [1] => blue
    [2] => green
    [3] => red
    [4] => brown
    [5] => green
)

Note: When using non-numeric array keys array_merge works a little differently. It will actually overwrite values with identical keys. This can be good, but don’t let it catch you off guard.

7. array_pop

array_pop actually has a couple of use cases. You can use it to shorten an array by one and you can use it to retrieve the last element in an array. Be careful though because it modifies the array either way.

Code

$array = ['red', 'blue', 'green'];

print_r(array_pop($array));
print_r($array);

Output

green

Array
(
    [0] => red
    [1] => blue
)

When you want to find a specific value within an array or you want to check whether the value exists, array_search can be very useful. It returns the key corresponding to the found value.

Code

$array = ['red', 'blue', 'green'];
print_r(array_search('blue', $array));

Output

1

Note: If an item is not found, array_search will return false but if the item is found at index 0 then it will return 0. This is one of those cases where strict type checking becomes important.

9. array_reduce

When you want to convert an array into a single value or string, add up all the values in an array, or something like that, array_reduce can come in handy.

Code

$array = ['red', 'blue', 'green'];
print_r(array_reduce($array, function ($carry, $item) {
    return $carry . " " . $item;
}));

Output

red blue green

Note: If you just want to convert an array into a string with separators as in the above example, you’re probably better off using implode, but array_reduce is still good for more complex conversions.

10. array_slice

I find myself frequently trying to extract the beginning or end of an array, so array_slice has come in handy a number of times. It allows you to take a cut of an array by specifying an offset and length.

Code

$array = ['red', 'blue', 'green'];
// First element in an array
print_r(array_slice($array, 0, 1)) . 
;
// Last element in an array
print_r(array_slice($array, -1, 1)) . 
;
// Second two elements
print_r(array_slice($array, 1, 2)) . 
;

Output

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

Note: array_slice will reset your keys by default, but it has a fourth parameter that you can set to retain keys.

11. array_values

Similar to array_keys there is a function to get just the values from an array and reset the indices to their numerical defaults. array_values allows you to pass in an array and get only the values of each item back, which can be useful if you’ve put your array into some custom order and want the indices to reflect that.

Code

$array = ['a' => 'red', 'b' => 'blue', 'c' => 'green'];
print_r(array_values($array));

Output

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

12. count

Another common task when dealing with arrays is determining the length of the array. count can actually be used for many different variable types, but I find it most useful for counting the number of elements in an array.

Code

$array = ['red', 'blue', 'green'];

print_r(count($array));

Output

3

Note: You can also set count to COUNT_RECURSIVE which means it will count the number of sub-elements within an array of arrays. Check out the documentation for details.

13. in_array

Rather than looping over an array to check whether or not a value appears in the array, you can simply call in_array and let PHP do the work. This function will return a boolean true if it finds the value and false if it does not.

Code

$array = ['red', 'blue', 'green'];
print_r(in_array('blue', $array));

Output

1

14. sort/ksort/usort

There are a number of built-in sorting functions for arrays in PHP, but I’ll limit myself to three of the most common. First, sort will compare each value in your array and order them from lowest to highest. Second, ksort will compare each key in your array and order them from lowest to highest. Finally, usort lets you define a function that will compare each value and do the sorting.

Code

// sort
$array = [10 => 90, 9 => 93, 7 => 92, 13 => 91];

sort($array);

print_r($array);

// ksort
$array = [10 => 90, 9 => 93, 7 => 92, 13 => 91];

ksort($array);

print_r($array);

// usort
$array = [10 => 90, 9 => 93, 7 => 92, 13 => 91];

usort($array, function ($a, $b) {
    // Sorts by reverse numerical order
    return $a < $b;
});

print_r($array);

Output

Array
(
    [0] => 90
    [1] => 91
    [2] => 92
    [3] => 93
)
Array
(
    [7] => 92
    [9] => 93
    [10] => 90
    [13] => 91
)
Array
(
    [0] => 93
    [1] => 92
    [2] => 91
    [3] => 90
)

Note: In each of these functions the array is passed by reference, meaning the function modifies the array directly and doesn’t return the modified array. Keep this in mind if you want to keep a copy of your original array.

If you’d like to see more array functions or learn more about arrays in PHP, be sure to check out the manual.

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