Hash/digest with determined (small) amount of variants

Question

I need to get only 16 (or other small number) of possible hashes from string for color-coding contacts based on contact name.

I had try to get a crc32 hash and then take a first symbol, which is hex digit:

$contact = 'Robin Hood';
$colors = [
     '0' => 'F8BBD0',
     '1' => 'E1BEE7',
     ...
     'e' => 'D7CCC8',
     'f' => 'CFD8DC',
];
$firstLetter = hash('crc32', $contact)[0];
return '#' . $colors[$firstLetter];

However, I have doubts about good distribution of such method. How can I get small and determined amount of variants digest from string?

score 1 · Accepted Answer · edited May 23 '17 at 12:31

If your primary concern is good distribution I would use a good pseudo random engine:

$colorKey = bin2hex(openssl_random_pseudo_bytes(1))[0];
return '#' . $colors[$colorKey];

I can't say how this compares to the distribution of the first char of a hash, but this will definitely work well for your purposes.

Edit: Since you require a hash, I tested various hashes against a text file of 500 random names and found crc32 to have the most even distribution. I don't know how many names you expect or how good a distribution you require, but your solution seems like a good choice to me:

<?php
function sd_square($x, $mean) { return pow($x - $mean,2); }

function sd($array) {
    return sqrt(array_sum(array_map("sd_square", $array, array_fill(0,count($array), (array_sum($array) / count($array)) ) ) ) / (count($array)-1) );
}

$crcColorCounts = array_fill_keys(range(0, 15), 0);
$file = fopen('random_names.txt', 'r');
while ($contact = fgets($file)) {
    $hash = hash('crc32', $contact);
    $letter = $hash[0];
    $crcColorCounts[hexdec($letter)]++;
}
fclose($file);
print_r($crcColorCounts);
echo 'Standard deviation: ', sd($crcColorCounts);

Output:

Array
(
    [0] => 32
    [1] => 26
    [2] => 33
    [3] => 31
    [4] => 40
    [5] => 29
    [6] => 33
    [7] => 20
    [8] => 33
    [9] => 30
    [10] => 39
    [11] => 27
    [12] => 36
    [13] => 33
    [14] => 29
    [15] => 30
)
Standard deviation: 4.8815127436755

(Standard deviation function taken from this answer.)

I also tried MD5, SHA1, and the last char of CRC32. All returned standard deviations around 7, making the first char of CRC32 the winner.

No, my task is not getting random, but every time same (permanent) hash for same person, based on the name of this person. — vatavale, Apr 02 '16 at 05:28
@vatavale Please see my edit. I tested the distribution of the hash. — Matt S, Apr 02 '16 at 15:24

Hash/digest with determined (small) amount of variants

1 Answers1