PHP prepend associative array with literal keys?
Is it possible to prepend an associative array with literal key=>value pairs? I know that array_unshift() works with numerical keys, but I'm hoping for something that will work with literal keys.
As an example I'd like to do the following:
$array1 = array('fruit3'=>'apple', 'fruit4'=>'orange');
$array2 = array('fruit1'=>'cherry', 'fruit2'=>'blueberry');
// prepend magic
$resulting_array = ('fruit1'=>'cherry',
'fruit2'=>'blueberry',
'fruit3'=>'apple',
'fruit4'=>'orange');
Can't you just do:
$resulting_array = $array2 + $array1;
?
You cannot directly prepend an associative array with a key-value pair.
However, you can create a new array that contains the new key-value pair at the beginning of the array with the union operator +. The outcome is an entirely new array though and creating the new array has O(n) complexity.
The syntax is below.
$new_array = array('new_key' => 'value') + $original_array;
Note: Do not use array_merge(). array_merge() overwrites keys and does not preserve numeric keys.
In your situation, you want to use array_merge():
array_merge(array('fruit1'=>'cherry', 'fruit2'=>'blueberry'), array('fruit3'=>'apple', 'fruit4'=>'orange'));
To prepend a single value, for an associative array, instead of array_unshift(), again use array_merge():
array_merge(array($key => $value), $myarray);
Using the same method as @mvpetrovich, you can use the shorthand version of an array to shorten the syntax.
$_array = array_merge(["key1" => "key_value"], $_old_array);
References:
As of PHP 5.4 you can also use the short array syntax, which replaces array() with [].
@Cletus is spot on. Just to add, if the ordering of the elements in the input arrays are ambiguous, and you need the final array to be sorted, you might want to ksort:
$resulting_array = $array1 + $array2;
ksort($resulting_array);
ksort returns boolean, so the above needs to be done as two statements not one, e.g. $a = $array1 + $array2; ksort($a);, otherwise $resulting_array will be a boolean value not the array you were expecting.
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