Split/group array elements by field

Question

For a game, I have a collection of 'houses' and each house belongs to a 'city'. I want to separate this collection (it's an array) based on this city, so each city will have its own array of houses. I found no built-in array function to do this (such as an array_split taking a callback), so how would I do this?

I thought on iterating over every element of the array, but this seems very very slow. The houses are already all ordered by city id, so I may use some splitting function if I get the exact position where the city id changes.

Houses in the array are stored like this:

array(3) {
    ["id"]=> string(1) "1",
    ["name"]=> string(13) "Example House",
    ["city_id"]=> string(1) "1",
}

Cities are just a number representing them, not another object.

I expect the out to be something like:

array(n) {
    [1]=> array(o) {
        ["id"]=> string(1) "1",
        ["name"]=> string(13) "Example House",
    }, ...
}

Is it the correct manner to do it? Is there any builtin function or better algorithm?

Answer 1

It's pretty hard to work on your structure without looping it.. Maybe you can simplify it like this..

$new_arr = array();
foreach($arr as $arr1)
{
    $new_arr[$arr1['id']] = array_slice($arr1,1);
}
print_r($new_arr);

Demonstration

Eventhough this can be achieved using array functions , but performance will not be that good when compared to a foreach