Custom sorting array of arrays using two conditions

Question

I have the following array:

$arr = [
    [
        'user_id' => 1,
        'product_id' => 1
    ],
    [
        'user_id' => 1,
        'product_id' => 2
    ],
    [
        'user_id' => 1,
        'product_id' => 3
    ],
    [
        'user_id' => 2,
        'product_id' => 1
    ],
    [
        'user_id' => 2,
        'product_id' => 2
    ],
    [
        'user_id' => 3,
        'product_id' => 1
    ]
];

And I want to sort it so it looks like this:

$arr = [
    [
        'user_id' => 1,
        'product_id' => 1
    ],
    [
        'user_id' => 2,
        'product_id' => 1
    ],
    [
        'user_id' => 3,
        'product_id' => 1
    ],
    [
        'user_id' => 1,
        'product_id' => 2
    ],
    [
        'user_id' => 2,
        'product_id' => 2
    ],
    [
        'user_id' => 1,
        'product_id' => 3
    ]
];

So basically I need to order by product_id and user_id in such a way that it selects the lower number product_id from each user before proceeding to the next.

I tried to use usort but I couldn't get it to work.

usort($campaigns, function($a, $b){
    if($a['product_id'] == $b['product_id']){
        return 0;
    }

    if($a['product_id'] < $b['product_id']){

        if($a['user_id'] == $b['user_id']){
            return 1;
        }

        if($a['user_id'] < $a['user_id']){
            return 0;
        }

        return -1;
    }else{

        if($a['user_id'] == $a['user_id']){
            return -1;
        }

        if($a['user_id'] < $a['user_id']){
            return 0;
        }

        return 1;
    }
});

I also tried array_multisort but all I could get it to do is to order using the same order that I already retrieve from the database.

Answer 1

Assumption is your values is integers:

usort($campaigns, function($a, $b){
    if($a['product_id'] == $b['product_id']){
        return $a['user_id'] - $b['user_id'];
    } else {
        return $a['product_id'] - $b['product_id'];
    }
});

---

Also you can use database ordering with ORDER BY product_id, user_id clause.