Get highest and lowest values from an array where order is like "AAA", "AA", "A", "BBB", "BB", etc

Question

What I'm trying to do is creating a custom rating system like this:

AAA - Highest rating
AA
A
BBB
BB
B
CCC
CC
C - Lowest rating

In which AAA is the highest and C the lowest. For this this to work I need PHP to know which rating is the highest, lowest and everything in between and evaluate series of ratings based on that. I allready figured out how to create a sorting with usort() like so:

$ratings = array("a" => "AAA", "b" => "AA", "c" => "A", "d" => "BBB", "e" => "BB", "f" => "B", "g" => "CCC", "h" => "CC", "i" => "C");
$sortedRatings = usort($ratings, "cmp_function");

This will return an array neatly sorted from highest priority to lowest. Now I need to go ahead and use this sorting to get the highest and lowest rating from an array like this one:

$ratingHistory = array("BB", "B", "CCC", "C", "BB");

So how could I go about getting the highest and lowest value from $ratingHistory based on the sorting as in $sortedRatings ? I hope someone can help me out with this one. If my problem isn't completely clear to you, drop a comment so I can try to explain further.

Edit:

Just to be clear. The expected outcomes would be:

Highest: BB
Lowest: C

If you can sort the array, then Highest value is first key, Lowest is last key. — fusion3k, Mar 29 '16 at 14:22
How about sorting and selecting the first and last element of the array? That would be effective and simple but not very efficient. — jojonas, Mar 29 '16 at 14:23

score 2 · Accepted Answer · answered Mar 29 '16 at 15:16

This solution works with your original $ratings array and — through usort() — sort $ratingHistory:

$ratings = array("a" => "AAA", "b" => "AA", "c" => "A", "d" => "BBB", "e" => "BB", "f" => "B", "g" => "CCC", "h" => "CC", "i" => "C");
$ratingHistory = array("BB", "B", "CCC", "C", "BB");

usort
(
    $ratingHistory,
    function( $a, $b ) use( $ratings )
    {
        return strcmp( array_search( $a, $ratings ), array_search( $b, $ratings ) );
    }
);

$result = array( 'max'=>current($ratingHistory), 'min'=>end($ratingHistory) );

print_r( $result );

Will print:

Array
(
    [max] => BB
    [min] => C
)

Performance:

I have compared the performance of above example with a foreach(), an array_map() (all cases with both associative and enumerated array as $ratings and with different $ratingHistory sizes). The usort() method is in anyhow far the more efficient. This because you have anyway to iterate complete array, but with usort you can use less commands/functions/comparisons.

Both solutions work, but this is better performance wise indeed :) — Frank Kluytmans, Mar 30 '16 at 07:12

Vincent Decaux · Answer 2 · 2016-03-29T17:43:56.600

1

You can try this code :

$ratings = array("", "AAA","AA", "A", "BBB", "BB", "B", "CCC", "CC", "C");
$ratingHistory = array("BB", "B", "CCC", "C", "BB");

$min = 0;
$max = INF;
foreach ($ratingHistory as $row)
{
    $rate = array_search($row, $ratings);
    if ($rate && $rate > $min) {
        $min = $rate;
    }
    if ($rate && $rate < $max) {
        $max = $rate;
    }
}

echo 'Min : '. $ratings[$min];
echo '<br />Max : '. $ratings[$max];

If you test, the values are BB and C for your example.

edited Mar 29 '16 at 17:43

answered Mar 29 '16 at 14:30

Vincent Decaux

9,857
6
56
84

This seems to work fine except for it doesn't recognize AAA as the highest rating. I'm working on a solution for that and will post it when found. Thanks for your answer, I will accept it when I'm able to complete it ;) – Frank Kluytmans Mar 29 '16 at 14:56
Yes, weird. You can put an empty string in $ratings before the "AAA". It solves this problem. Look to my edit. – Vincent Decaux Mar 29 '16 at 17:43

mickmackusa · Answer 3 · 2022-08-01T05:45:41.773

Because ALL of your encounterable values are in your ratings lookup array, you can enjoy the sweet brevity of array_intersect(). This will remove all values from the $ratings array which are not found in the $ratingsHistory array. Of course, the $ratings array is already in order, so the results are instantly accessible from the first and last elements.

Code: (Demo)

$ratingHistory = array_intersect($ratings, $ratingHistory);
var_export([
    'min' => $ratingHistory[key($ratingHistory)],
    'max' => $ratingHistory[array_key_last($ratingHistory)]
]);

If you don't want to maintain a lookup array (to allow your code to be more dynamic/robust and require less maintenance), spell out the logic. Using a linear foreach loop will have a smaller time complexity and will offer better performance than a non-linear sort like usort().

Code: (Demo)

$result = ['min' => null, 'max' => null];
foreach ($array as $value) {
    if (
        !$result['min']
        || (!trim($value, $result['min']) ? $value < $result['min'] : $value > $result['min'])
    ) {
        $result['min'] = $value;
    }
    if (
        !$result['max']
        || (!trim($value, $result['max']) ? $value > $result['max'] : $value < $result['max'])
    ) {
        $result['max'] = $value;
    }
}
var_export($result);

Maintaining a lookup array for priorities and calling usort() is also a clean approach, but this has been asked before on Stack Overflow and it will have the poorest time complexity score of these three snippets. 1 2 3 4

Code: (Demo)

$lookup = array_flip($ratings);
usort($ratingHistory,  fn($a, $b) => $lookup[$a] <=> $lookup[$b]);
var_export([
    'min' => $ratingHistory[0],
    'max' => $ratingHistory[array_key_last($ratingHistory)]
]);

P.s. Any technique that is making iterated calls of array_search() will have worse performance than ALL of my snippets above. "Value searching" an array is always going to be slower than "key searching" an array in PHP.

Get highest and lowest values from an array where order is like "AAA", "AA", "A", "BBB", "BB", etc

3 Answers3

Performance: