Sort rows of a multidimensional array using two columns nested in each row's subarray

Question

I am trying to sort this array by array[key]['premium']['Monthly'] and if there are two Monthly prices the same, then sort by quarterly, then semi-annual, then annual.

I search and couldn't figure out how to use array_multisort() function.

Array (
    [0] => Array (
        [product_id] => 1
        [rate] => 27.07
        [premium] => Array (
            [Annual] => 436.05
            [Semi-Annual] => 226.75
            [Quarterly] => 115.6
            [Monthly] => 37.11
        )
    )
    [1] => Array (
        [product_id] => 2
        [rate] => 35.00
        [premium] => Array (
            [Annual] => 565
            [Semi-Annual] => 293.8
            [Quarterly] => 149.73
            [Monthly] => 50.85
        )    
    )
    [2] => Array (
        [product_id] => 3
        [rate] => 30.52
        [premium] => Array (
            [Annual] => 497.8
            [Monthly] => 47.29
        )
    )
)

Answer 1

I think you want to use usort function, something like

function compare($a, $b){
  $p1 = $a["premium"];
  $p2 = $b["premium"];
  if($p1["Monthly"] == $p2["Monthly"]){
     // compare by quarterly
     ...
  }else{
     if($p1["Monthly"] < $p2["Monthly"])then return -1;
     else return 1;
  }
}

usort($prices, "compare");

where $prices is your array. The comparision function isn't implemented fully, just to show the idea. Also, since it looks like there might be missing items in the price array (ie last one misses Quarterly and Semi-Annual) you have to check first (before comparison) does the items exists and take appropriate action in case one or both are missing.