PHP Using array keys to store data

Question

Suppose I need to add and remove elements from an array where they must be unique.

Class A {
    protected $elements = [];

    function add($element) {
        if (!in_array($element, $this->elements)) {
            $this->elements[] = $element;
        }
    }

    function remove($element) {
        if (($key = array_search($element, $this->elements)) !== false) {
            unset($this->elements[$key]);
        }
    }
}

This looks fine but if $elements has a great deal of elements in it PHP will need to iterate every time add() or remove() is called. Instead I can do this:

Class A {
    protected $elements = [];

    function add($element) {
        $this->elements[$element] = true;
    }

    function remove($element) {
        unset($this->elements[$element]);
    }
}

Which should be performing at the same speed regardless of the number of elements, but I may be completely wrong about this and that is the point of this question.

I have been doing this all over the place in my codes but it is bugging me that I am storing a bunch of useless information (in this example some true booleans) that serve absolutely no purpose but can not go without them. This appears as some kind of a flaw and makes me thing that this method is not completely bulletproof as I may think.

Is this way of storing information in arrays any better than the, what I suppose would be considered the proper way, first example and are there any downsides to it, except storing needless information?

score 1 · Answer 1 · answered Jul 20 '16 at 16:44

1

Your second solution will be significantly faster than the first one.

The downsides are that it will take significantly more memory and that you can store only integers and strings like that.

If you are doing a lot of add/remove on reasonably high number of elements - then go with the second solution.

If you are expecting hundreds of thousands or even million of elements - then the second solution may go with out of memory exception - so you should use the first one.

answered Jul 20 '16 at 16:44

Alexandar Mitsev

293
1
7

Why would the second solution take up more memory? Is it because of hashing the keys? – php_nub_qq Jul 20 '16 at 16:49
yes, when php arrays are used as hash tables - they take more memory – Alexandar Mitsev Jul 20 '16 at 16:54
But sequential arrays are also hash tables, why would such an array take up less space than an associative one :? – php_nub_qq Jul 20 '16 at 16:57
They are handled differently in the background – Alexandar Mitsev Jul 20 '16 at 17:03
But unless you have insane amount of elements you will never have problem with memory, so the second solution is perfect. – Alexandar Mitsev Jul 20 '16 at 17:34

PHP Using array keys to store data

1 Answers1