Programming PHP, 2nd Edition

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

The array_diff( ) function identifies values from one array that are not present in others:

    $diff = array_diff(array1, array2 [, array ... ]);

For example:

 $a1 = array('bill', 'claire', ...