Array Operators

Table 6.8. Array Operators

Example	Name	Result
$a + $b	Union	Union of $a and $b.
$a == $b	Equality	`TRUE` if $a and $b have the same key/value pairs.
$a === $b	Identity	`TRUE` if $a and $b have the same key/value pairs in the same order and of the same types.
$a != $b	Inequality	`TRUE` if $a is not equal to $b.
$a <> $b	Inequality	`TRUE` if $a is not equal to $b.
$a !== $b	Non-identity	`TRUE` if $a is not identical to $b.

The + operator appends elements of remaining keys from the right handed array to the left handed, whereas duplicated keys are NOT overwritten.

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<?php

$a = array("a" => "apple", "b" => "banana");
$b = array("a" => "pear", "b" => "strawberry", "c" => "cherry");

$c = $a + $b; // Union of $a and $b
echo "Union of \$a and \$b: \n";
var_dump($c);

$c = $b + $a; // Union of $b and $a
echo "Union of \$b and \$a: \n";
var_dump($c);
?>

When executed, this script will print the following:

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Union of $a and $b:

array(3) {

  ["a"]=>

  string(5) "apple"

  ["b"]=>

  string(6) "banana"

  ["c"]=>

  string(6) "cherry"
}
Union of $b and $a:

array(3) {

  ["a"]=>

  string(4) "pear"

  ["b"]=>

  string(10) "strawberry"

  ["c"]=>

  string(6) "cherry"
} ?>

Elements of arrays are equal for the comparison if they have the same key and value.

Example 6.7. Comparing arrays

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<?php

$a = array("apple", "banana");
$b = array(1 => "banana", "0" => "apple");

var_dump($a == $b); // bool(true)
var_dump($a === $b); // bool(false)
?>

See also the manual sections on the Array type and Array functions.

Code Examples / Notes » language.operators.array

When comparing arrays that have (some or all) element-values that are themselves array, then in PHP5 it seems that == and === are applied recursively - that is * two arrays satisfy == if they have the same keys, and the values at each key satisfy == for whatever they happen to be (which might be arrays); * two arrays satisfy === if they have the same keys, and the values at each key satisfy === for whatever (etc.). Which explains what happens if we compare two arrays of arrays of arrays of... Likewise, the corresponding inversions for != <> and !==. I've tested this to array-of-array-of-array, which seems fairly convincing. I've not tried it in PHP4 or earlier.

The code from texbungalow at web dot de below is slightly incorrect. If my memory from primary school history is correct, roman numerals don't allow things like MIM - it has to be MCMXCIX, ie each step is only 1 level down (sorry, I can't explain it very well. a print_r($segments) comparing the snippets should explain. Corrected code: <?php function roman ($nr ) { $base_digits= array ( 1=> "I", 10=> "X", 100=> "C", 1000=> "M", ); $help_digits= array ( 5=> "V", 50=> "L", 500=> "D", ); $all_digits= $base_digits+ $help_digits; foreach ($base_digits as $key1=> $value1 ) foreach ($all_digits as $key2=> $value2 ) if ($key1< $key2 && $key1 >= ($key2 / 10)) $segments[$key2- $key1 ]= $value1. $value2; $segments+= $all_digits; krsort ($segments ); foreach ($segments as $key=> $value ) while ($key<= $nr ) { $nr-= $key; $str.= $value; } return $str; } echo roman (1998); // prints MCMXCVIII ?>

Array Operators

Table 6.8. Array Operators

Example 6.7. Comparing arrays

Code Examples / Notes » language.operators.array

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