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

Solution:

This solution works with your original$ratings array and — throughusort() — sort$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 );
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Will print:

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

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

Solution:

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

Solution:

Because ALL of your encounterable values are in your ratings lookup array, you can enjoy the sweet brevity ofarray_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)]
]);
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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 likeusort().

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);
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Maintaining a lookup array for priorities and callingusort() 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)]
]);
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P.s. Any technique that is making iterated calls ofarray_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.