How to sort array based on parameter

Question

I have the JSON like this:

{
    "class": {
        "type": "major",
        "order": "1"
    },
    "number": {
       "type": "date",
       "order": "5"
    },
    "amount": {
        "type": "date",
        "order": "3"
    },
}

I need to make that into PHP array and sort based on order field.

If the number is same then the order should stay as it is.

EDIT:

Also if some of the elements don't have order then they should come at bottom

@SergiuParaschiv can u please add some answer for stable sorting — user3147180, Feb 21 '14 at 18:33
I don't see anything in your question about stable sorting. For the edit part you can just assume `order = PHP_INT_MAX ` if it's undefined. — Sergiu Paraschiv, Feb 21 '14 at 18:43
Also: http://stackoverflow.com/questions/4353739/preserve-key-order-stable-sort-when-sorting-with-phps-uasort — Sergiu Paraschiv, Feb 21 '14 at 18:45
@SergiuParaschiv A stable sort is necessitated by the need to not change the existing order of elements that compare equal - it is definitely required. — George Brighton, Feb 21 '14 at 18:50

George Brighton · Accepted Answer · 2014-02-21T18:48:05.147

You can use json_decode() to convert it to a PHP array. You'll then need to write a stable implementation of usort() to sort the values. Something like this:

function stableSort(array $array) {
    // turn the input array into something we can more easily manipulate
    $lookup = array();
    $i = 0;
    foreach($array as $key => $value) {
        $lookup[] = array(
                'position' => $i++,
                'key' => $key,
                'value' => $value);
    }

    usort($lookup, function(array $a, array $b) {
        if(!isset($a['value']['order'])) {
            if(!isset($b['value']['order'])) {
                return $a['position'] > $b['position'];
            }
            return 1;
        }

        if(!isset($b['value']['order'])) {
            return -1;
        }

        if($a['value']['order'] == $b['value']['order']) {
            return $a['position'] > $b['position'];
        }

        return $a['value']['order'] > $b['value']['order'] ? 1 : -1;
    });

    // recreate the original array
    $sorted = array();
    foreach($lookup as $element) {
        $sorted[$element['key']] = $element['value'];
    }

    return $sorted;
}

$array = json_decode($json, true);
$sorted = stableSort($array);

We never return 0 from within the comparison function, as that would break the guarantee of a stable sort. The first two if statements exist to handle the cases where the order key does not exist in one or both of the inputs.

will it work, if some of the fields dont have order key. i want to put them at bottom — user3147180, Feb 21 '14 at 18:22
@ziollek The OP never specifies that in his requirements - he only says the order must remain the same if `order` *is* present. — George Brighton, Feb 21 '14 at 18:55

ziollek · Answer 2 · 2014-02-21T18:51:32.153

you should decode json to array, and then use usort to sort array:

$data = '{
    "class": {
        "type": "major",
        "order": "1"
    },
    "number": {
       "type": "date",
       "order": "5"
    },
    "amount": {
        "type": "date",
        "order": "3"
    }
}';

$array = json_decode($data, true);
usort($array, function ($left, $right) {
  if ($left['order'] == $right['order']) {
    return 0;
  }
  return $left['order'] < $right['order'] ? -1 : 1;
});

var_dump($array);

To guarantee stable sort, you need to index elements before sorting, and use that index while comparing "equal" elements. I also add some conditions to move elements with empty order to bottom (but with preserving change of it primary sequence):

$i = 0;
foreach ($array as $key => $value) {
  $array[$key]['original_order'] = $i;
  $i++;
}

uasort($array, function ($left, $right) {
  if (isset($left['order'])) {
    if(isset($right['order'])) {
      if ($right['order'] == $left['order']) {
        return $left['original_order'] < $right['original_order'] ? -1 : 1;
      }
      return $left['order'] < $right['order'] ? -1 : 1;
    }
    return -1;
  } elseif(isset($right['order'])) {
    return 1;
  } else {
    return $left['original_order'] < $right['original_order'] ? -1 : 1;
  }
});

foreach ($array as $key => $value) {
  unset($array[$key]['original_order']);
}

-1: `If the number is same then the order should stay as it is`. `usort()` may change the order of elements that compare equal. — George Brighton, Feb 21 '14 at 18:19
will it work, if some of the fields dont have order key. i want to put them at bottom — user3147180, Feb 21 '14 at 18:23
seriously... do not hijack other answers to add a copy of your answer there. — John Dvorak, Feb 21 '14 at 18:56

How to sort array based on parameter

2 Answers2