How to keep the previous values in array after new assignment? - php

Question

I have an array named $arr = array. Some of its keys has value, like this:
$arr['1'] = 'one';
$arr['2'] = 'two';
$arr['3'] = 'three';
Now I initialize that array with another arry, some thing like this:
$arr = array('4' => 'four', '5' => 'five');
But I need to keep the previous values. I mean is, when I print that array, the output will be like this:
echo '<pre>';
print_r($arr);
/* ---- output:
Array
(
[4] => four
[5] => five
)
*/
While I want this output:
Array
(
[1] => one
[2] => two
[3] => three
[4] => four
[5] => five
)
So, How can I take care of old keys (values) after re-initialized?

Answer 1

Here are your options detailed below: array_merge, union (+ operator), array_push, just set the keys directly and make a function that just loops over the array with your own custom rules.
Sample data:
$test1 = array('1'=>'one', '2'=>'two', '3'=>'three', 'stringkey'=>'string');
$test2 = array('3'=>'new three', '4'=>'four', '5'=>'five', 'stringkey'=>'new string');
array_merge (as seen in other answers) will re-index numeric keys (even numeric strings) back to zero and append new numeric indexes to the end. Non numeric string indexes will overwrite the value where the index exists in the former array with the value of the latter array.
$combined = array_merge($test1, $test2);
Result (http://codepad.viper-7.com/c9QiPe):
Array
(
[0] => one
[1] => two
[2] => three
[stringkey] => new string
[3] => new three
[4] => four
[5] => five
)
A union will combine the arrays but both string and numeric keys will be handled the same. New indexes will be added and existing indexes will NOT be overwritten.
$combined = $test1 + $test2;
Result (http://codepad.viper-7.com/8z5g26):
Array
(
[1] => one
[2] => two
[3] => three
[stringkey] => string
[4] => four
[5] => five
)
array_push allows you to append keys to an array. So as long as the new keys are numeric and in sequential order, you can push on to the end of the array. Note though, non-numeric string keys in the latter array will be re-indexed to the highest numeric index in the existing array +1. If there are no numeric keys, this would be zero. You would also need to reference each new value as a separate argument (see arguments two and three below). Also, since the first argument is taken in by reference, it will modify the original array. The other options allow you to combine to a separate array in case you need the original.
array_push($test1, 'four', 'five');
Result (http://codepad.viper-7.com/5b9nvC):
Array
(
[1] => one
[2] => two
[3] => three
[stringkey] => string
[4] => four
[5] => five
)
You could also just set the keys directly.
$test1['4'] = 'four';
$test1['5'] = 'five';
Or even just make a loop and wrap it in a function to handle your custom rules for merging
function custom_array_merge($arr1, $arr2){
//loop over array 2
foreach($arr2 as $k=>$v){
//if key exists in array 1
if(array_key_exists($arr1, $k)){
//do something special for when key exists
} else {
//do something special for when key doesn't exists
$arr1[$k] = $v;
}
}
return $arr1;
}
The function could be expanded to use stuff like func_get_args to allow any number of arguments.
I'm sure there are also more "hacky" ways to do it using stuff like array_
splice or other array functions. However, IMO, I would avoid them just to keep the code a little more clear about what you are doing.

Answer 2

use array_merge:
$arr = array_merge($arr, array('4' => 'four', '5' => 'five'));
Well, as per the comments (which are correct) this will reindex the array, another solution to avoid that would be to do as follows:
array_push($arr, "four", "five");
But this would not work if you have different keys, like strings that are not masked numbers.
Another way is to use + in order to merge them maintaining keys:
$arr['1'] = 'one';
$arr['2'] = 'two';
$arr['3'] = 'three';
$arr2 = array('4' => 'four', '5' => 'five');
$arr = $arr + $arr2;

Answer 3

Another way to do it, and keeps the keys of the array, is using array_replace.
$arr['1'] = 'one';
$arr['2'] = 'two';
$arr['3'] = 'three';
print_r(array_replace($arr, array('4' => 'four', '5' => 'five')));
Output:
Array
(
[1] => one
[2] => two
[3] => three
[4] => four
[5] => five
)