Php – Sorting by Color

colorsPHPsorting

I have a long list (1000+) of hex colors broken up in general color categories (Red, Orange, Blue, etc). When I show the list of colors in each category I need to show them in order of shade. i.e. light red first and dark red last.

What would the algorithm be to do this? (googling has failed me)

Best Answer

I know this question is old, but I didn't found a pretty solution to this problem, so I investigate a little bit and want to share what I did for hypothetical future googlers.

First, convert to HSL is a great idea. But sort only by hue or light didn't solve completely the issue when your color are not "classified".

Given an array which look like:

$colors = [
            [ 'color' => '#FDD4CD'],
            [ 'color' => '#AE3B3B'],
            [ 'color' => '#DB62A0'],
            ...
          ]

First we convert all Hex colors to HSL

foreach ($colors as &$color) {
       $color['hsl'] = hexToHsl($color['color']);
}


/**
 * Convert a hexadecimal color in RGB
 * @param string $hex
 * @return array
 */
function hexToHsl($hex){
    list($r, $g, $b) = sscanf($hex, "#%02x%02x%02x");
    return rgbToHsl($r, $g, $b);
}

/**
 * Convert a RGB color in its HSL value
 * @param int $r red
 * @param int $g green
 * @param int $b blue
 * @return array
 */
function rgbToHsl($r, $g, $b)
{
    $r /= 255;
    $g /= 255;
    $b /= 255;

    $max = max($r, $g, $b);
    $min = min($r, $g, $b);

    $h = 0;
    $l = ($max + $min) / 2;
    $d = $max - $min;

    if ($d == 0) {
        $h = $s = 0; // achromatic
    } else {
        $s = $d / (1 - abs(2 * $l - 1));

        switch ($max) {
            case $r:
                $h = 60 * fmod((($g - $b) / $d), 6);
                if ($b > $g) {
                    $h += 360;
                }
                break;

            case $g:
                $h = 60 * (($b - $r) / $d + 2);
                break;

            case $b:
                $h = 60 * (($r - $g) / $d + 4);
                break;
        }
    }
    return array('h' => round($h, 2), 's' => round($s, 2), 'l' => round($l, 2));
}

Then sort colors

We compare:

Their hue if they are in the same 'interval' (This help to understand why I choose 30°). So we compare the hue only if both are in [0-30], [30-60], [60-90],...
If not in the same interval, sort by their Lightness, then by saturation if both share the same Lightness.

So:

usort($colors, function ($a, $b) {
    //Compare the hue when they are in the same "range"
    if(!huesAreinSameInterval($a['hsl']['h'],$b['hsl']['h'])){
       if ($a['hsl']['h'] < $b['hsl']['h'])
           return -1;
       if ($a['hsl']['h'] > $b['hsl']['h'])
           return 1;
    }
    if ($a['hsl']['l'] < $b['hsl']['l'])
        return 1;
    if ($a['hsl']['l'] > $b['hsl']['l'])
        return -1;
    if ($a['hsl']['s'] < $b['hsl']['s'])
         return -1;
    if ($a['hsl']['s'] > $b['hsl']['s'])
          return 1;
    return 0;
 });

/**
 * Check if two hues are in the same given interval
 * @param float $hue1
 * @param float $hue2
 * @param int $interval
 * @return bool
 */
function huesAreinSameInterval($hue1, $hue2, $interval = 30){
    return (round(($hue1 / $interval), 0, PHP_ROUND_HALF_DOWN) === round(($hue2 / $interval), 0, PHP_ROUND_HALF_DOWN));
}

rgbToHsl found on www.brandonheyer.com

hexToRgb found on stackoverflow

Related Solutions

Javascript – Sorting an array of objects by property values

Sort homes by price in ascending order:

homes.sort(function(a, b) {
    return parseFloat(a.price) - parseFloat(b.price);
});

Or after ES6 version:

homes.sort((a, b) => parseFloat(a.price) - parseFloat(b.price));

Some documentation can be found here.

For descending order, you may use

homes.sort((a, b) => parseFloat(b.price) - parseFloat(a.price));

Javascript – Sorting object property by values

Move them to an array, sort that array, and then use that array for your purposes. Here's a solution:

var maxSpeed = {
    car: 300, 
    bike: 60, 
    motorbike: 200, 
    airplane: 1000,
    helicopter: 400, 
    rocket: 8 * 60 * 60
};
var sortable = [];
for (var vehicle in maxSpeed) {
    sortable.push([vehicle, maxSpeed[vehicle]]);
}

sortable.sort(function(a, b) {
    return a[1] - b[1];
});

//[["bike", 60], ["motorbike", 200], ["car", 300],
//["helicopter", 400], ["airplane", 1000], ["rocket", 28800]]

Once you have the array, you could rebuild the object from the array in the order you like, thus achieving exactly what you set out to do. That would work in all the browsers I know of, but it would be dependent on an implementation quirk, and could break at any time. You should never make assumptions about the order of elements in a JavaScript object.

var objSorted = {}
sortable.forEach(function(item){
    objSorted[item[0]]=item[1]
})

In ES8, you can use Object.entries() to convert the object into an array:

const maxSpeed = {
    car: 300, 
    bike: 60, 
    motorbike: 200, 
    airplane: 1000,
    helicopter: 400, 
    rocket: 8 * 60 * 60
};

const sortable = Object.entries(maxSpeed)
    .sort(([,a],[,b]) => a-b)
    .reduce((r, [k, v]) => ({ ...r, [k]: v }), {});

console.log(sortable);

In ES10, you can use Object.fromEntries() to convert array to object. Then the code can be simplified to this:

const maxSpeed = {
    car: 300, 
    bike: 60, 
    motorbike: 200, 
    airplane: 1000,
    helicopter: 400, 
    rocket: 8 * 60 * 60
};

const sortable = Object.fromEntries(
    Object.entries(maxSpeed).sort(([,a],[,b]) => a-b)
);

console.log(sortable);