array_rand() array to string? - php

Question

I have an array, such like:
$hex = array("0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f");
I want to return 6 random elements as a string (eg. 1a3564):
$random_color = array_rand($hex,6);
I thought imploding $random_color would do the trick:
echo implode($random_color);
But array_rand() stores positions of elements in parent array, not this array elements, so I get something like:
259111213 instead of 259bcd.
I know this does exactly what I want:
echo $hex[$random_color[0]];
echo $hex[$random_color[1]];
echo $hex[$random_color[2]];
echo $hex[$random_color[3]];
echo $hex[$random_color[4]];
echo $hex[$random_color[5]];
But:
is there any way to store array elements within array_rand()? Why it stores elements' positions instead of elements in the first place?
what's the best way to do what I want to achieve?
why does array_rand() NEVER choose a letter as the first element, and almost never as the second/third (99% of generated colors look like 11111a 12345c 123456)?

Answer 1

Random colors should be generated in simplier way:
printf('%02x%02x%02x',mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));
or
printf('%06x',mt_rand(0,16777215));
If you need to save color to variable, use sprintf instead of printf

Answer 2

Since the items are all different, you can turn them into keys rather than values, then use array_rand on the result:
implode('', array_rand(array_flip($hex), 6));
However, there may be a better way of achieving your overall goal. For example, if the overall goal allows for repetitions of digits, simply generate a random number from 0 through 0xFFFFFF and convert to a hex string:
dechex(mt_rand(0, 0xFFFFFF));
Why it stores elements' positions instead of elements in the first place?
From the manual page:
This is done so that you can pick random keys as well as values out of the array.
why does array_rand() NEVER choose a letter as the first element, and almost never as the second/third (99% of generated colors look like 11111a 12345c 123456)?
array_rand uses rand (php_rand, in the C source). Depending on your system, php_rand is rand, random or lrand48. rand is a particularly poor random number generator.

Answer 3

array_rand() returns the keys of the randomly picked elements (see manual, section Return Values).
In order for it to work as expected, use array_flip() to retrieve the keys:
$random_color = array_rand(array_flip($hex), 6);
As for the "strange" results where there are almost no letters first elements, IDEOne and my server seem to reproduce these findings. A local machine running in my office (still running Debian etch / PHP 5.2.9) seems to disagree and evenly distribute elements from $hex... Seems to be a PHP version thing?

Answer 4

you are close try this:
$hex = array("0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f");
shuffle($hex);
echo sub_str(implode('',$hex),0,6);

Answer 5

If you don't need to maintain the order of the $hex array, you could substitute this with shuffle(). Something like this (codepad example):
<?php
$hex = array("0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f");
shuffle($hex);
echo implode(array_slice($hex, 0, 6));

Answer 6

If you just want a random string of hex digits, you could also do something like
substr(md5(time()),-6);
or
substr(md5(uniqid()),-6);
You would get similar results without having to mess with the array.

Answer 7

is there any way to store array elements within array_rand()? Why it
stores elements' positions instead of elements in the first place?
According to array_rand documentation, it returns the array 'keys', not the 'values'. Since your array is not an associative array, the keys are numbers. You'd need to do (untested):
$result = "";
$random_color = array_rand($hex, 6);
foreach ($random_color as $randomIndex) {
$result = $result . $hex[$randomIndex];
}
Don't use array shuffle or array_rand because elements cannot repeat with that approach. That's not what you are trying to do.
what's the best way to do what I want to achieve?
If you want to generate a random color, you can use:
$color = '';
while(strlen($c) < 6) {
$color .= sprintf("%02X", mt_rand(0, 255));
}
why does array_rand() NEVER choose a letter as the first element, and
almost never as the second/third (99% of generated colors look like
11111a 12345c 123456)?
You may need to initialize the random numbers generator, but this is just a guess (see Timur's comment to this answer).
mt_srand((double)microtime()*1000000);