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Unit 7: Multidimensional Arrays

function reverseCompare($x, $y) Notes
{
if ( $x[2] == $y[2] )

return 0;
else if ( $x[2] < $y[2] )

return 1;
else
return -1;
}

Calling usort($products, reverse Compare) would now result in the array being placed in
descending order by price.

The user-defined sorts do not have reverse variants, but you can sort a
multidimensional array into reverse order by the comparison function.

7.6 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, all using built-in
functions.
7.6.1 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’)
7.6.2 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

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