Question

I am trying to create a new array from two current arrays. Tried array_merge, but it will not give me what I want. $array1 is a list of keys that I pass to a function. $array2 holds the results from that function, but doesn’t contain any non-available resuls for keys. So, I want to make sure that all requested keys comes out with ‘null’:ed values, as according to the shown $result array.

It goes a little something like this:

$array1 = array('item1', 'item2', 'item3', 'item4');

$array2 = array(
    'item1' => 'value1',
    'item2' => 'value2',
    'item3' => 'value3'
);

Here’s the result I want:

$result = array(
    'item1' => 'value1',
    'item2' => 'value2',
    'item3' => 'value3',
    'item4' => ''  
);

It can be done this way, but I don’t think that it’s a good solution – I really don’t like to take the easy way out and suppress PHP errors by adding @:s in the code. This sample would obviously throw errors since 'item4' is not in $array2, based on the example.

foreach ($keys as $k => $v){
    @$array[$v] = $items[$v]; 
}

So, what’s the fastest (performance-wise) way to accomplish the same result?

Answer 1

array_fill_keys will build you a nice array you can use in array_merge:

array_merge(array_fill_keys($array1, ''), $array2);

Or, instead of array_merge, you can use the + op which performs a union:

$array2 + array_fill_keys($array1, '');

This one works with numerical keys or mixed numerical/strings 🙂