Array find min value with user-defined comparison compare function

Question

My user defined comparison compare function is defined with an array:

$boardkey_to_values=Array(19=>2601248,23=>2601248,39=>2603445,
 43=>2256319,47=>2632006,59=>2603445,63=>2232152,67=>2260713,71=>2632006,...)

so 23>19 EDIT:23=19, 39>19, 39<23,...

I have an array of values $board_id, and I want to get the array of all the keys for the minimum values.

Here's my solution, but I don't think it is really intuitive.

$min_key=Array(0);
foreach ($board_id as $key => $value) {
if ($boardkey_to_values[$board_id[$min_key[0]]]>$boardkey_to_values[$value])
 $min_key=Array($key);
if ($boardkey_to_values[$board_id[$min_key[0]]]==$boardkey_to_values[$value] && $min_key[0]!=$key)
 $min_key[]=$key;
}

Here is an example to show how this should behave:

say $board_id = [19,23,39,47,71]

it will look at the values corresponding to this numbers [2601248,2601248,2603445,2632006,2632006]

it looks for the smallest value: 2601248

so the result ($min_key should be [19,23])

• David Harkness: Why is 23 > 19 when they both map to the same value? Shouldn't they be equal?
• edi9999: Yes you're right 23=19, I have edited my question

Answer 1

This should be O(n)* where n is count($board_id).

$mapped = array_map(function ($id) use ($boardkey_to_values) {
 return array($boardkey_to_values[$id], $id);
}, $board_id);
asort($mapped);
list($min_value, $id) = reset($mapped);
$min_ids = array($id);
while (list($value, $id) = next($mapped)) {
 if ($value == $min_value) {
 $min_ids[] = $id;
 }
 else {
 break;
 }
}

* ignoring the call to asort which is probably O(n log n).

• edi9999: What exactly does the use keyword do after the parameters of an anonymous function ?
• David Harkness: It allows the anonymous function to access the named variable. Without it the function can only access the local variables and arguments it declares.

Answer 2

You could try doing it this way:

$min_key = null;
asort($boardkey_to_values);
foreach(array_count_values($boardkey_to_values) as $val) {
 $min_key = array_slice( array_keys($boardkey_to_values), $val );
 break;
}

I believe that would accomplish what you're trying to do.

• edi9999: Your function is very slow compared to mine, because array_slice is slow given the size of the $boardkey_to_values (more than 40 000 entries). And it isn't exactly what I meant (cf edit for the example)