Programming PHP

Sets
Arrays let you implement the basic operations of set theory: union, intersection, and
difference. Each set is represented by an array, and various PHP functions implement
the set operations. The values in the set are the values in the array—the keys
are not used, but they are generally preserved by the operations.
The union of two sets is all the elements from both sets, with duplicates removed.
The array_merge( ) and array_unique( ) functions let you calculate the union. Here’s
how to find the union of two arrays:
function array_union($a, $b) {
$union = array_merge($a, $b); // duplicates may still exist
$union = array_unique($union);
return $union;
}
$first = array(1, 'two', 3);
$second = array('two', 'three', 'four');
$union = array_union($first, $second);
print_r($union);
Array
(
[0] => 1
[1] => two
[2] => 3
[4] => three
[5] => four
)
The intersection of two sets is the set of elements they have in common. PHP’s builtin
array_intersect( ) function takes any number of arrays as arguments and returns
an array of those values that exist in each. If multiple keys have the same value, the
first key with that value is preserved.
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 this, returning an array with values from the first array that are
not present in the second.
The following code takes the difference of two arrays:
$first = array(1, 'two', 3);
$second = array('two', 'three', 'four');
$difference = array_diff($first, $second);
print_r($difference);
Array
(
[0] => 1
[2] => 3
)
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Using Arrays | 137