how to add elements to an array in a loop using php

Question

I am dynamically trying to populate a multidimensional array and having some trouble.

I have a list of US states. Associative array like this $states[nc], $states[sc

Answer 1

foreach($states as $state) {
    $data[$state] = $state;

    foreach($state->cities as $city) {
      $data[$state][] = $city;
    }
}

Using empty brackets adds an element to the array.