Question

I have an associative array of the form:

$input = array("one" => <class object1>,
               "two" => <class object2,
               ... //and so on);

The keys of $input are guaranteed to be unique. I also have a method called moveToHead($key) which moves the $input[$key] element to the 0th location of this associative array. I have few questions:

1. Is it possible to determine the index of an associative array?
2. How to move the array entry for corresponding $key => $value pair to the index 0 and retaining the $key as is?
3. What could be the best possible way to achieve both of the above points?

I was thinking to do array_flip for 2nd point (a sub solution), but later found out that array_flip can only be done when array elements are int and string only. Any pointers?

Answer 1

With a function called array_keys you can determine the index of a key:

$keys = array_flip(array_keys($input));
printf("Index of '%s' is: %d\n", $key, $keys[$key]);

To insert an array at a certain position (for example at the beginning), there is the array_splice function. So you can create the array to insert, remove the value from the old place and splice it in:

$key = 'two';
$value = $input[$key];
unset($input[$key]);    
array_splice($input, 0, 0, array($key => $value));

Something similar is possible with the array union operator, but only because you want to move to the top:

$key = 'two';
$value = $input[$key];
unset($input[$key]);
$result = array($key => $value) + $input;

But I think this might have more overhead than array_splice.