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Last updated: Fri, 27 Jun 2008

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


<?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:

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 #1 Comparing arrays


<?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.

Type Operators

String Operators

Last updated: Fri, 27 Jun 2008

add a note User Contributed Notes
Array Operators

csaba at alum dot mit dot edu
24-Jun-2008 09:54


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);



$aSum = array_add($a1, $a2, $a3);

$aDiff = array_subtract($a1, $a2, $a3);



// $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

csaba at alum dot mit dot edu
13-Dec-2007 02:42


Simple array arithmetic:

If you want to add or subtract the elements at identical keys...



<?php

function array_add($a1, $a2) {  // ...

  // adds the values at identical keys together

  $aRes = $a1;

  $aRays = func_get_args();

  for ($i=1;$i<sizeof($aRays);++$i) {

    $aRay = $aRays[$i];

    foreach ($aRay as $key => $val)

      if (array_key_exists($key, $aRes))

        $aRes[$key] += $aRay[$key];

    $aRes += $aRay; }

  return $aRes; }



function array_subtract($a1, $a2) {  // ...

  // subtracts the values at identical keys from the corresponding value in $a1

  $aRes = $a1;

  $aRays = func_get_args();

  for ($i=1;$i<sizeof($aRays);++$i) {

    $aRay = $aRays[$i];

    foreach ($aRay as $key => $val) {

      if (array_key_exists($key, $aRes)) $aRes[$key] -= $aRay[$key];

      else $aRes[$key] = -$aRay[$key]; } }

  return $aRes; }



Example:

$a1 = array(9, 8, 7);

$a2 = array(1=>7, 6, 5);

$a3 = array(2=>5, 4, 3);



$aSum = array_add($a1, $a2, $a3);

$aDiff = array_subtract($a1, $a2, $a3);



// $aSum  => [9, 15, 18, 9, 3]

// $aDiff => [9, 1, -4, -9, -3]

?>



To make a similar function, array_concatenate(), change the first += only in array_add() to .=

Csaba Gabor from Vienna

Q1712 at online dot ms
20-Apr-2007 06:54


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)

?>

puneet singh @ value-one dot com
18-Jan-2006 11:42


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 )

kit dot lester at lycos dot co dot uk
21-Aug-2005 10:01


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.

kit dot lester at lycos dot co dot uk
21-Aug-2005 09:44


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.

Peter
29-Oct-2004 08:57


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

?>

dfranklin at fen dot com
22-Apr-2004 02:40


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

texbungalow at web dot de
26-Apr-2003 07:46


use '+=' to quickly append an array to another one:



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 ) 

                        $segments[$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 (888);   //  prints DCCCLXXXVIII

amirlaher AT yahoo DOT co SPOT uk
09-Dec-2002 11:41


[]= 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 )

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Type Operators

String Operators

Last updated: Fri, 27 Jun 2008