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Programming PHP, 3rd Edition by Peter MacIntyre, Kevin Tatroe, Rasmus Lerdorf

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Acting on Entire Arrays

PHP has several useful functions for modifying or applying an operation to all elements of an array. You can merge arrays, find the difference, calculate the total, and more; this can all be accomplished by using built-in functions.

Calculating the Sum of an Array

The array_sum() function adds up the values in an indexed or associative array:

$sum  = array_sum(array);

For example:

$scores = array(98, 76, 56, 80);
$total = array_sum($scores); // $total = 310

Merging Two Arrays

The array_merge() function intelligently merges two or more arrays:

$merged = array_merge(array1, array2 [, array ... ])

If a numeric key from an earlier array is repeated, the value from the later array is assigned a new numeric key:

$first  = array("hello", "world"); // 0 => "hello", 1 => "world"
$second = array("exit", "here");   // 0 => "exit",  1 => "here"

$merged = array_merge($first, $second);
// $merged = array("hello", "world", "exit", "here")

If a string key from an earlier array is repeated, the earlier value is replaced by the later value:

$first  = array('bill' => "clinton", 'tony' => "danza");
$second = array('bill' => "gates", 'adam' => "west");

$merged = array_merge($first, $second);
// $merged = array('bill' => "gates", 'tony' => "danza", 'adam' => "west")

Calculating the Difference Between Two Arrays

Another common function to perform on a set of arrays is to get the difference; that is, the values in one array that are not present in another array. The array_diff() function calculates ...

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