PHP Tutorial - PHP array_merge() function

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Definition

The array_merge() function combines two or more arrays. array_merge() renumbers numerical indexes and merges string indexes.

Syntax

PHP array_merge() function has the following syntax.

Parameter

Note

If you want to join two or more arrays together to produce one big array, you need the array_merge() function.

array_merge() joins the array elements of the arrays together to produce the final array. array_push(), array_unshift(), and the square bracket syntax all insert array arguments to produce multidimensional arrays:

<?PHP
$authors = array( "Java", "PHP" ); 
$moreAuthors = array( "CSS", "MySQL" ); 
array_push( $authors,  $moreAuthors ); 
print_r( $authors );   
?>

The code above generates the following result.

array_merge() preserves the keys of associative arrays, so we can use it to add new key/value pairs to an associative array:

<?PHP
    $myBook = array( "title" =>  "Learn PHP from java2s.com", 
                     "author" =>  "java2s.com", 
                     "pubYear" =>  2000 ); 

    $myBook = array_merge( $myBook, array( "numPages" =>  464 ) ); 

    print_r ( $myBook );   
?>

The code above generates the following result.

Example 1

If you add a key/value pair using a string key existing in the array, the original element gets overwritten. This makes array_merge() useful for updating associative arrays:

<?PHP
    $myBook = array( "title" =>  "Learn PHP from java2s.com", 
                     "author" =>  "java2s.com", 
                     "pubYear" =>  2000 ); 

    $myBook = array_merge( $myBook, array( "title" =>  "java from java2s.com", "pubYear" =>  1952 ) ); 
    print_r ( $myBook );   
?>

The code above generates the following result.

Example 2

An element with the same numeric key doesn't get overwritten; instead the new element is added to the end of the array and given a new index:

<?PHP
         $authors = array( "Java", "PHP", "CSS", "HTML" ); 
         $authors = array_merge( $authors, array( 0 =>  "MySQL" ) ); 

         print_r ( $authors );   
?>

The code above generates the following result.

Example 3

Use array_merge() to reindex an indexed array by passing the array as the parameter. This ensures that all the elements of an indexed array are consecutively indexed:

<?PHP
$authors = array( 4 =>  "Java", 2 =>  "PHP", 5 =>  "CSS", 7 =>  "HTML" ); 
print_r( array_merge( $authors ) );    
?>

The code above generates the following result.

Example 4

Merge associate array

<?php
$toppings1 = array("A", "B", "C", "D");
$toppings2 = array("D", "java2s.com", "PHP");
$both_toppings = array_merge($toppings1, $toppings2);

var_dump($both_toppings);
?>

The code above generates the following result.

Example 5

The + operator in PHP is overloaded so that you can use it to merge arrays, e.g., $array3 = $array1 + $array2. If PHP finds any keys in the second array that clash with the keys in the first array, they will be skipped.

<?PHP
$arr1 = array("A"=>1, "B"=>2, "C"=>3);
$arr2 = array("B"=>3, "C"=>8);
$arr3 = $arr1 + $arr2;
var_dump(array_merge($arr1, $arr2));
?>

The code above generates the following result.

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