Sort array by two object properties using anonymous function

Question

I have the following array:

Array
(
    [0] => stdClass Object
        (
            [timestamp] => 1
            [id] => 10
        )

    [1] => stdClass Object
        (
            [timestamp] => 123
            [id] => 1
        )

    [2] => stdClass Object
        (
            [timestamp] => 123
            [id] => 2
        )

)

I'm currently using the following code to sort the array by the timestamp property:

function sort_comments_by_timestamp(&$comments, $prop)
{
    usort($comments, function($a, $b) use ($prop) {
        return $a->$prop < $b->$prop ? 1 : -1;
    });
}

How can I also sort id by id descending when timestamp is the same?

Is there a reason why you call it _by_timestamp, but also have a $prop parameter? — Matthew
– Matthew, Commented Dec 22, 2011 at 0:37
@Matthew other than I was doing some tests and bad naming? No :) Already fixed it btw — PeeHaa
– PeeHaa, Commented Dec 22, 2011 at 0:40

Andreas Helgegren · Accepted Answer · 2011-12-22 00:52:03Z

23

Suggestion is to send in an array with $props

function sort_comments_by_timestamp(&$comments, $props)
{
    usort($comments, function($a, $b) use ($props) {
        if($a->$props[0] == $b->$props[0])
            return $a->$props[1] < $b->$props[1] ? 1 : -1;
        return $a->$props[0] < $b->$props[0] ? 1 : -1;
    });
}

And then call it with

sort_comments_by_timestamp($unsorted_array,array("timestamp","id"));

If you want it to work with X number of $props you can make a loop inside the usort always comparing a property with its preceding property in the array like this:

function sort_comments_by_timestamp(&$comments, $props)
{
    usort($comments, function($a, $b) use ($props) {
        for($i = 1; $i < count($props); $i++) {
            if($a->$props[$i-1] == $b->$props[$i-1])
                return $a->$props[$i] < $b->$props[$i] ? 1 : -1;
        }
        return $a->$props[0] < $b->$props[0] ? 1 : -1;
    });
}

Cheers!

answered Dec 22, 2011 at 0:52

Andreas Helgegren

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1 Comment

Marek Skiba Over a year ago

If you get error: Array to string conversion you need to replace all $a->$props[X] to $a->{$props[X]}

Matthew · Accepted Answer · 2011-12-22 00:29:05Z

4

function sort_comments_by_timestamp(&$comments, $prop)
{
    usort($comments, function($a, $b) use ($prop) {
        if ($a->$prop == $b->$prop)
          return $b->id - $a->id;
        else
          return $a->$prop < $b->$prop ? 1 : -1;
    });
}

The above sorts first by the $prop parameter and then secondary by id.

answered Dec 22, 2011 at 0:29

Matthew

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Comments

woru · Accepted Answer · 2015-01-16 16:33:32Z

3

You can do it with ouzo goodies (I know you've heard about it :P).

$result = Arrays::sort($array,
    Comparator::compound(
        Comparator::compareBy('timestamp'),
        Comparator::compareBy('id')
    )
);

answered Jan 16, 2015 at 16:33

woru

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Comments

Dylan Grech · Accepted Answer · 2017-04-04 06:32:45Z

3

I know this is fairly old question however didn't find much info for when you want to sort by multiple properties kinda like mySQL ORDERBY does so here's a function from a personal framework

Option 1: order($key, $direction='asc') where $key is a property of the objects and $direction is 'asc' or 'desc'

Option 2: order(array($key => $direction, $key => $direction)) This is similar to option 1 however when 2 objects have the same value for $key, the second sort option from the array passed is used.

public function order($arr, $key=null, $direction='ASC'){
    if(!is_string($key) && !is_array($key))
        throw new InvalidArgumentException("order() expects the first parameter to be a valid key or array");

    $props = array();

    if(is_string($key)) {
        $props[$key] = strtolower($direction) == 'asc' ? 1 : -1;
    }else{
        $i = count($key);
        foreach($key as $k => $dir){
            $props[$k] = strtolower($dir) == 'asc' ? $i : -($i);
            $i--;
        }
    }

    usort($arr, function($a, $b) use ($props){
        foreach( $props as $key => $val ){
            if( $a->$key == $b->$key ) continue;
            return $a->$key > $b->$key ? $val : -($val);
        }
        return 0;
    });

    return $arr;

}

edited Apr 4, 2017 at 6:32

answered Apr 4, 2017 at 6:16

Dylan Grech

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2 Comments

Victor D. Over a year ago

Very nice little function. I was using the accepted answer for my sorting needs (with some personal tweaks) and it decided to stop working after a CMS update of the website. This saved me a bunch of time trying to debug what the problem is/was.

Dylan Grech Over a year ago

Glad it helped out :)

dqhendricks · Accepted Answer · 2011-12-22 00:27:26Z

2

$result = -1;
if ($a->timestamp < $b->timestamp) {
   $result = 1;
} else if ($a->timestamp === $b->timestamp) {
   if ($a->id < $b->id) $result = 1;
}
return $result;

Put this within the usort closure. You can also get rid of the $prop argument and the use ($prop) part.

answered Dec 22, 2011 at 0:27

dqhendricks

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Comments

Tomas Votruba · Accepted Answer · 2018-07-22 15:59:43Z

2

      function compare_city($a, $b)
      {
        // sort by state
        $retval = strnatcmp($a->state, $b->state);
        // if identical, sort by city
        if(!$retval) $retval = strnatcmp($a->city, $b->city);
        return $retval;
      }

      // sort alphabetically by state and city
      usort($sortable, __NAMESPACE__ . '\compare_city');

This function worked with me! Answer found at: Sorting SimpleXMLElement Object arrays

edited Jul 22, 2018 at 15:59

Tomas Votruba

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answered Jun 17, 2018 at 12:57

Kash

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1 Comment

John Rix Over a year ago

A number of the answers above (including the accepted answer!) seem to miss the 'equal' outcome for comparisons. Nice to see use of strnatcmp to handle this properly, in particular for string properties. Also don't forget strnatcasecmp for the case insensitive equivalent.

dareapersven · Accepted Answer · 2018-10-09 01:48:43Z

The accepted answer has a loop variant that will not always work.

if($a->$props[$i-1] == $b->$props[$i-1])
     return $a->$props[$i] < $b->$props[$i] ? 1 : -1;

obj1 prop1:foo, prop2: bar, prop3: test

obj2 prop1:foo, prop2: bar, prop3: apple

At $i = 1, the first comparison is true, and as bar is not less than bar, it will return -1 rather than continue with the loop to evaluate prop3.

Just an FYI.

I have a variant that also takes direction, so each property can also be sorted by ascending or descending order using -1 and 1, respectively.

function sortByProps(&$anArray, $props) {
    usort($anArray, function($a, $b) use ($props) {
        for($i = 0; $i < count($props); $i++) {
            if( $a->{$props[$i][0]} < $b->{$props[$i][0]}) {
                return $props[$i][1];
            }
            else if( $a->{$props[$i][0]} > $b->{$props[$i][0]}) {
                return -1* $props[$i][1];
            }
        }
        return 0;
    });
}

sortByProps($someArray,(array(['name',-1],['address',-1],['occupation',-1],['favorite_food',-1])));

goat · Accepted Answer · 2021-03-12 19:58:05Z

1

Here's how to sort by an arbitrary number of criteria, one after the other, breaking ties. It works a lot like an sql order by col1, col2 clause.

I always forget if $a - $b vs $b - $a sorts ascending or descending. Adjust as needed.

$comparatorSequence = array(
    function($a, $b) { return $a->timestamp - $b->timestamp; }
  , function($a, $b) { return $a->id - $b->id; }
);

usort($theArray, function($a, $b) use ($comparatorSequence) {
    foreach ($comparatorSequence as $cmpFn) {
        $diff = call_user_func($cmpFn, $a, $b);
        if ($diff !== 0) {
            return $diff;
        }
    }
    return 0;
});

edited Mar 12, 2021 at 19:58

answered Dec 22, 2011 at 1:55

goat

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