Question

here is my array sample $data[][];

Array( [0] => Array ( [id] => 1349
                      [rating1] => 1.9378838029981E-7
                      [rating2] => 1.1801796607774     )
       [1] => Array ( [id] => 1350
                      [rating1] => 5.5499981876923E-7
                      [rating2] => 1.5121329727308     )
       [2] => Array ( [id] => 1377
                      [rating1] => 0.00023952225410117
                      [rating2] => 2.1947077830236     )
       [3] => Array ( [id] => 1378
                      [rating1] => 0.00022982302863634
                      [rating2] => 2.2135588326622     )
       [4] => Array ( [id] => 1379
                      [rating1] => 0.00026272979843585
                      [rating2] => 2.2388295595073     )
       [5] => Array ( [id] => 1380
                      [rating1] => 0.0002788640872546
                      [rating2] => 2.1815325502993     )
)

I want to find max($data[][rating?]) but return $data[id][max_rating?] i.e. id associated with the max value.
Finding the max was easy for one particular, say rating1, I used array_reduce as follows (this is inspired from this SO ):

$max = array_reduce($data, function($a, $b) {
    return $a > $b['rating1'] ? $a : $b['rating1']; 
});

Now I have two questions :
1. How can I extend above array_reduce to include rating2 ? I have other ratingX as well.
2. I do not want the max value, rather the $data[][id] associated with the max.

I am not so much concerned about Q1, but the second one is important as I don’t want to search through the array again to get associated $data[][id].
One line of thought is to use array_map instead of array_reduce, but I couldn’t come up with a version which will pass on both [id] and [rating?]. Also, there are complications when I try to max() multiple rating? at one shot, as each rating will have different max, which in turn associates with different [id].
EDIT : Just to be clear, I want all the respective ids associated with respective max of each rating?

Answer 1

assuming your array is unsorted you have to loop through it at least once (either manually or using builtin functions). i’d use the following code:

$array = array(
  array( 'id' => 1349, 'sudhi_rating1' => 1.9378838029981E-7, 'sudhi_rating2' => 1.1801796607774 ),
  array( /* … */ ),
  /* … */
);

$idx_max = 0;
foreach($array as $idx => $item) {
  if($item['sudhi_rating1'] > $array[$idx_max]['sudhi_rating1'])
    $idx_max = $idx;
}

echo "Rating 1 has max value at id ", htmlspecialchars($array[$idx_max]['id']);

you can extend the code to check multiple ratings at once (make $idx_max an array itself and add more ifs):

$idx_max = array (
  'sudhi_rating1' => 0,
  'sudhi_rating2' => 0,
  /* … */ );
foreach($array as $idx => $item) {
  foreach($idx_max as $rating => &$max) {
    if($item[$rating] > $array[$max][$rating])
      $max = $idx;
  }
}

foreach($idx_max as $rating => $max)
  echo 'Max value for ', htmlspecialchars($rating), ' has id ', htmlspeciachars($array[$max]['id']);