Wednesday, 7 August 2013

17 useful functions for manipulating arrays in PHP

This document outlines some of the more useful functions in the PHP array toolkit, and features detailed explanations and usage examples.
Like arrays in other languages, PHP arrays allow you to store multiple values in a single variable and operate on them as a set. PHP offers an extensive array manipulation toolkit—over 60 functions—that lets you process arrays in almost any way imaginable including reversing them, extracting subsets, comparing and sorting, recursively processing, and searching them for specific values.
This document outlines some of the more useful functions in the PHP array toolkit, with explanations and usage examples:
This table is also available as free downloadable PDF.

Function
Explanation
Example
sizeof($arr)
 This function returns the number of elements in an array.
Use this function to find out how many elements an array contains; this information is most commonly used to initialize a loop counter when processing the array.
 Code:
$data = array("red", "green", "blue");

echo "Array has " . sizeof($data) . " elements";
?>

Output:
Array has 3 elements
array_values($arr)
 This function accepts a PHP array and returns a new array containing only its values (not its keys). Its counterpart is the array_keys() function.
Use this function to retrieve all the values from an associative array.
 Code:
$data = array("hero" => "Holmes", "villain" => "Moriarty");
print_r(array_values($data));
?>

Output:
Array
(
[0] => Holmes
[1] => Moriarty
)
array_keys($arr)
 This function accepts a PHP array and returns a new array containing only its keys (not its values). Its counterpart is the array_values() function.
Use this function to retrieve all the keys from an associative array.
 Code:
$data = array("hero" => "Holmes", "villain" => "Moriarty");
print_r(array_keys($data));
?>

Output:
Array
(
[0] => hero
[1] => villain
)
array_pop($arr)
 This function removes an element from the end of an array.
 Code:
$data = array("Donald", "Jim", "Tom");
array_pop($data);
print_r($data);
?>

Output:
Array
(
[0] => Donald
[1] => Jim
)
array_push($arr, $val)
 This function adds an element to the end of an array.
 Code:
$data = array("Donald", "Jim", "Tom");
array_push($data, "Harry");
print_r($data);
?>

Output:
Array
(
[0] => Donald
[1] => Jim
[2] => Tom
[3] => Harry
)
array_shift($arr)
 This function removes an element from the beginning of an array.
 Code:
$data = array("Donald", "Jim", "Tom");
array_shift($data);
print_r($data);
?>

Output:
Array
(
[0] => Jim
[1] => Tom
)
array_unshift($arr, $val)
 This function adds an element to the beginning of an array.
 Code:
$data = array("Donald", "Jim", "Tom");
array_unshift($data, "Sarah");
print_r($data);
?>

Output:
Array
(
[0] => Sarah
[1] => Donald
[2] => Jim
[3] => Tom
)
each($arr)
 This function is most often used to iteratively traverse an array. Each time each() is called, it returns the current key-value pair and moves the array cursor forward one element. This makes it most suitable for use in a loop.
 Code:
$data = array("hero" => "Holmes", "villain" => "Moriarty");
while (list($key, $value) = each($data)) {
echo "$key: $value \n";
}
?>

Output:
hero: Holmes
villain: Moriarty
sort($arr)
 This function sorts the elements of an array in ascending order. String values will be arranged in ascending alphabetical order.
Note: Other sorting functions include asort(), arsort(), ksort(), krsort() and rsort().
 Code:
$data = array("g", "t", "a", "s");
sort($data);
print_r($data);
?>

Output:
Array
(
[0] => a
[1] => g
[2] => s
[3] => t
)
array_flip($arr)
 The function exchanges the keys and values of a PHP associative array.
Use this function if you have a tabular (rows and columns) structure in an array, and you want to interchange the rows and columns.
 Code:
$data = array("a" => "apple", "b" => "ball");
print_r(array_flip($data));
?>

Output:
Array
(
[apple] => a
[ball] => b
)
array_reverse($arr)
 The function reverses the order of elements in an array.
Use this function to re-order a sorted list of values in reverse for easier processing—for example, when you're trying to begin with the minimum or maximum of a set of ordered values.
 Code:
$data = array(10, 20, 25, 60);
print_r(array_reverse($data));
?>

Output:
Array
(
[0] => 60
[1] => 25
[2] => 20
[3] => 10
)
array_merge($arr)
 This function merges two or more arrays to create a single composite array. Key collisions are resolved in favor of the latest entry.
Use this function when you need to combine data from two or more arrays into a single structure—for example, records from two different SQL queries.
 Code:
$data1 = array("cat", "goat");
$data2 = array("dog", "cow");
print_r(array_merge($data1, $data2));
?>

Output:
Array
(
[0] => cat
[1] => goat
[2] => dog
[3] => cow
)
array_rand($arr)
 This function selects one or more random elements from an array.
Use this function when you need to randomly select from a collection of discrete values—for example, picking a random color from a list.
 Code:
$data = array("white", "black", "red");
echo "Today's color is " . $data[array_rand($data)];
?>

Output:
Today's color is red
array_search($search, $arr)
 This function searches the values in an array for a match to the search term, and returns the corresponding key if found. If more than one match exists, the key of the first matching value is returned.
Use this function to scan a set of index-value pairs for matches, and return the matching index.
 Code:
$data = array("blue" => "#0000cc", "black" => "#000000", "green" => "#00ff00");
echo "Found " . array_search("#0000cc", $data);
?>

Output:
Found blue
array_slice($arr, $offset, $length)
 This function is useful to extract a subset of the elements of an array, as another array. Extracting begins from array offset $offset and continues until the array slice is $length elements long.
Use this function to break a larger array into smaller ones—for example, when segmenting an array by size ("chunking") or type of data.
 Code:
$data = array("vanilla", "strawberry", "mango", "peaches");
print_r(array_slice($data, 1, 2));
?>

Output:
Array
(
[0] => strawberry
[1] => mango
)
array_unique($data)
 This function strips an array of duplicate values.
Use this function when you need to remove non-unique elements from an array—for example, when creating an array to hold values for a table's primary key.
 Code:
$data = array(1,1,4,6,7,4);
print_r(array_unique($data));
?>

Output:
Array
(
[0] => 1
[3] => 6
[4] => 7
[5] => 4
)
array_walk($arr, $func)
 This function "walks" through an array, applying a user-defined function to every element. It returns the changed array.
Use this function if you need to perform custom processing on every element of an array—for example, reducing a number series by 10%.
 Code:
function reduceBy10(&$val, $key) {
$val -= $val * 0.1;
}

$data = array(10,20,30,40);
array_walk($data, 'reduceBy10');
print_r($data);
?>

Output:
Array
(
[0] => 9
[1] => 18
[2] => 27
[3] => 36
)
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