Keith Devens .com

Updated function to merge two PHP arrays

I just noticed a search engine hit for my old PHP function to merge two arrays. Since I've been using updated code in my CMS for a while, I figured I'd at least post the new code here and supercede the old version.


<?php
function merge(&$a, &$b){
    if(is_array($a) and is_array($b) and !array_key_exists(0, $a)){
        $b_keys = array_keys($b);

        #for each key that exists in both arrays
        $keys = array_intersect(array_keys($a), $b_keys);
        foreach($keys as $key){
            merge($a[$key],$b[$key]);
        }

        #for every key in the second array that doesn't exist in the first
        $keys = array_diff($b_keys, $keys);
        foreach($keys as $key){
            $a[$key] = $b[$key];
        }
    }else{
        #either $a is a numeric array or $a or $b is a scalar,
        # so copy $b straight over $a
        $a = $b;
    }
}
?>

Update: I realized that (b - a) always equals (b - (a ^ b)), so instead of calculating (b - a), I updated the function to use (b - (a ^ b)) since I had already calculated (a ^ b) in the first step. Sorry... ^ is the closest I can get to ~~union~~ shit, intersection in ASCII.

Update: Here's yet another version. This one's much shorter and simpler. But I'll really have to time all three versions to find out which is the fastest. Though, I can't imagine this version being slower than the original one from the other post, since this one only has one loop and the other one has two.


<?php
function merge(&$a, &$b){
    if(is_array($a) and is_array($b) and !array_key_exists(0, $a)){
        #if both $a and $b are arrays, and $a isn't a numeric array
        while(list($key,) = each($b)){
            if(array_key_exists($key, $a)){
                merge($a[$key], $b[$key]);
            }else{
                $a[$key] = $b[$key];
            }
        }
        reset($b);
    }else{
        #if $a is a numeric array or $a or $b is a scalar
        # overwrite $a with $b
        $a = $b;
    }
}
?>

Permalink | 8 Comments | Tags: Programming | id 4059

04:19 (utc-4)
edited: 2003-07-11 01:01 (utc-4)

Comments

I realise this is a very old post, but just to let you know that there is a problem with the last merge function.

$arr1[0] = 15;
$arr1[2] = 30;

$arr2[1] = 45;
$arr2[3] = 60;

merge ($arr1, $arr2);

var_dump ($arr1);

Will delete all the values in $arr1 and replace them with $arr2 due to "!array_key_exists(0, $a)" in the first "if" statement.

Will delete all the values in $arr1 and replace them with $arr2 due to "!array_key_exists(0, $a)" in the first "if" statement.

Working as intended. It's meant to merge associative arrays, not normal arrays, and that's what the check is there for. Yes it's a kludge cause there's no sure way to know whether a PHP array is intended as an associative array or as a normal array.

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Thursday, July 10, 2003

Updated function to merge two PHP arrays

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