ScotlandPHP 2019

Array Operators

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 returns the right-hand array appended to the left-hand array; for keys that exist in both arrays, the elements from the left-hand array will be used, and the matching elements from the right-hand array will be ignored.

<?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);

\$a += \$b// Union of \$a += \$b is \$a and \$b
echo "Union of \\$a += \\$b: \n";
var_dump(\$a);
?>
When executed, this script will print the following:
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"
}
Union of \$a += \$b:
array(3) {
["a"]=>
string(5) "apple"
["b"]=>
string(6) "banana"
["c"]=>
string(6) "cherry"
}

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

Example #1 Comparing arrays

<?php
\$a
= array("apple""banana");
\$b = array(=> "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.

User Contributed Notes 13 notes

155
cb at netalyst dot com
10 years ago
The union operator did not behave as I thought it would on first glance. It implements a union (of sorts) based on the keys of the array, not on the values.

For instance:
<?php
\$a
= array('one','two');
\$b=array('three','four','five');

//not a union of arrays' values
echo '\$a + \$b : ';
print_r (\$a + \$b);

//a union of arrays' values
echo "array_unique(array_merge(\$a,\$b)):";
// cribbed from http://oreilly.com/catalog/progphp/chapter/ch05.html
print_r (array_unique(array_merge(\$a,\$b)));
?>

//output

\$a + \$b : Array
(
[0] => one
[1] => two
[2] => five
)
array_unique(array_merge(Array,Array)):Array
(
[0] => one
[1] => two
[2] => three
[3] => four
[4] => five
)
23
Q1712 at online dot ms
11 years ago
The example may get u into thinking that the identical operator returns true because the key of apple is a string but that is not the case, cause if a string array key is the standart representation of a integer it's gets a numeral key automaticly.

The identical operator just requires that the keys are in the same order in both arrays:

<?php
\$a
= array (0 => "apple", 1 => "banana");
\$b = array (1 => "banana", 0 => "apple");

var_dump(\$a === \$b); // prints bool(false) as well

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

var_dump(\$a === \$b); // prints bool(true)
?>
Dan Patrick
6 years ago
It should be mentioned that the array union operator functions almost identically to array_replace with the exception that precedence of arguments is reversed.
dfranklin at fen dot com
14 years ago
Note that + will not renumber numeric array keys.  If you have two numeric arrays, and their indices overlap, + will use the first array's values for each numeric key, adding the 2nd array's values only where the first doesn't already have a value for that index.  Example:

\$a = array('red', 'orange');
\$b = array('yellow', 'green', 'blue');
\$both = \$a + \$b;
var_dump(\$both);

Produces the output:

array(3) { [0]=>  string(3) "red" [1]=>  string(6) "orange" [2]=>  string(4) "blue" }

To get a 5-element array, use array_merge.

Dan
amirlaher AT yahoo DOT co SPOT uk
16 years ago
[]= could be considered an Array Operator (in the same way that .= is a String Operator).
[]= pushes an element onto the end of an array, similar to array_push:
<?
\$array= array(0=>"Amir",1=>"needs");
\$array[]= "job";
print_r(\$array);
?>
Prints: Array ( [0] => Amir [1] => needs [2] => job )
csaba at alum dot mit dot edu
10 years ago
Simple array arithmetic:
A more compact way of adding or subtracting the elements at identical keys...

<?php
function array_add(\$a1, \$a2) {  // ...
// adds the values at identical keys together

\$aRes = \$a1;
foreach (
array_slice(func_get_args(), 1) as \$aRay) {
foreach (
array_intersect_key(\$aRay, \$aRes) as \$key => \$val) \$aRes[\$key] += \$val;

\$aRes += \$aRay; }
return
\$aRes; }

function
array_subtract(\$a1, \$a2) {  // ...
// adds the values at identical keys together

\$aRes = \$a1;
foreach (
array_slice(func_get_args(), 1) as \$aRay) {
foreach (
array_intersect_key(\$aRay, \$aRes) as \$key => \$val) \$aRes[\$key] -= \$val;
foreach (
array_diff_key(\$aRay, \$aRes) as \$key => \$val) \$aRes[\$key] = -\$val; }
return
\$aRes; }

Example:
\$a1 = array(9, 8, 7);
\$a2 = array(1=>7, 6, 5);
\$a3 = array(2=>5, 4, 3);

// \$aSum  => [9, 15, 18, 9, 3]
// \$aDiff => [9, 1, -4, -9, -3]
?>

To make a similar function, array_concatenate(), change only the first of the two '+=' in array_add() to '.='
Csaba Gabor from Vienna
-1
xtpeqii at Hotmail dot com
1 year ago
\$a=[ 3, 2, 1];
\$b=[ 6, 5, 4];
var_dump( \$a + \$b );

output:
array(3) {
[0]=>
int(3)
[1]=>
int(2)
[2]=>
int(1)
}

The reason for the above output is that EVERY array in PHP is an associative one.
Since the 3 elements in \$b have the same keys( or numeric indices ) as those in \$a, those elements in \$b are ignored by the union operator.
-6
kit dot lester at lycos dot co dot uk
13 years ago
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.
-15
puneet singh @ value-one dot com
13 years ago
hi  just see one more example of union....

<?php
\$a
= array(1,2,3);
\$b = array(1,7,8,9,10);
\$c = \$a + \$b; // Union of \$a and \$b
echo "Union of \\$a and \\$b: \n";
//echo \$c
print_r(\$c);
?>
//output
Union of \$a and \$b: Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 9 [4] => 10 )
-19
sd6733531 at gmail dot com
5 years ago
Look out use + with array combine.

\$arr = array(1, 2, 3);
\$int=345;
\$arr=\$arr+\$int;

Of couse,use + to combine array is easy and readable.
But if one of the variable is not array type(like above code) ,that would make a PHP Fatal Error:
PHP Fatal error:  Unsupported operand types
Maybe should do check before.
-13
kit dot lester at lycos dot co dot uk
13 years ago
This manual page doesn't mention < & co for arrays, but example 15-2 in
http://www.php.net/manual/en/language.operators.comparison.php
goes to some lengths to explain how they work.
-2
drone dot ah at gmail dot com
1 year ago
The note about array comparison by Q1712 is not entirely accurate.

"The identical operator just requires that the keys are in the same order in both arrays:"

This may have been the case in past (I cannot verify it). It requires that the keys are in the same order AND that the values match

To extend that example

<?php

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

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

var_dump(\$a === \$b); // prints bool(false) as well

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

var_dump(\$a === \$b); // prints bool(true)

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

var_dump(\$a === \$b); // prints bool(false)

?>
-35
Anonymous
4 years ago
The manual say ...

"The + operator appends the right elements in the array from left, whereas duplicated keys are NOT overwritten"

but ..

\$a = array("a" => 'A', "b" => 'B');
\$b = array("a" => 'A', "b" => 'B', "c" => 'C');

\$c = \$a + \$b // or \$b + a  is  the same output;

echo '<pre>';

print_r(\$c);

echo '<pre>';

//Output   for  \$a + b  or  \$b + a
Array (
[a] => A
[b] => B
[c] => C
)