Programming PHP

Calling a Function for Each Array Element
PHP provides a mechanism, array_walk( ), for calling a user-defined function once
per element in an array:
array_walk(array, function_name);
The function you define takes in two or, optionally, three arguments: the first is the
element’s value, the second is the element’s key, and the third is a value supplied to
array_walk( ) when it is called. For instance, here’s another way to print table columns
made of the values from an array:
function print_row($value, $key) {
print("$value$key\n");
}
$person = array('name' => 'Fred', 'age' => 35, 'wife' => 'Wilma');
array_walk($person, 'print_row');
A variation of this example specifies a background color using the optional third
argument to array_walk( ). This parameter gives us the flexibility we need to print
many tables, with many background colors:
function print_row($value, $key, $color) {
print("$value$key\n");
}
$person = array('name' => 'Fred', 'age' => 35, 'wife' => 'Wilma');
array_walk($person, 'print_row', 'blue');
The array_walk( ) function processes elements in their internal order.
Reducing an Array
A cousin of array_walk( ), array_reduce( ), applies a function to each element of the
array in turn, to build a single value:
$result = array_reduce(array, function_name [, default ]);
The function takes two arguments: the running total, and the current value being
processed. It should return the new running total. For instance, to add up the
squares of the values of an array, use:
function add_up ($running_total, $current_value) {
$running_total += $current_value * $current_value;
return $running_total;
}
$numbers = array(2, 3, 5, 7);
$total = array_reduce($numbers, 'add_up');
// $total is now 87
The array_reduce( ) line makes these function calls:
add_up(2,3)
add_up(13,5)
add_up(38,7)
128 | Chapter 5: Arrays
This is the Title of the Book, eMatter Edition
Copyright © 2002 O’Reilly & Associates, Inc. All rights reserved.