array_rand() array to string?

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)?

"what's the best way to do what I want to achieve?" What's that? — outis
– outis, Commented Jan 13, 2012 at 14:20
@outis From the question "I want to return 6 random elements as a string (eg. 1a3564):" — Michael Mior
– Michael Mior, Commented Jan 13, 2012 at 14:22
@Michael: that's not the overarching goal. Did you read the linked page? — outis
– outis, Commented Jan 13, 2012 at 14:33
@Rufinus: there's still some things left out. For example, why can't there be repetitions of digits? Knowing the overall goal (what the colors are actually used for) would help quit e abit. — outis
– outis, Commented Jan 13, 2012 at 15:11

Timur · Accepted Answer · 2012-01-13 14:29:07Z

5

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

answered Jan 13, 2012 at 14:29

Timur

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Comments

outis · Accepted Answer · 2012-01-13 15:27:59Z

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.

Linus Kleen · Accepted Answer · 2012-01-13 14:33:37Z

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?

edited Jan 13, 2012 at 14:33

answered Jan 13, 2012 at 14:22

Linus Kleen

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Comments

Rufinus · Accepted Answer · 2012-01-13 14:25:19Z

2

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);

answered Jan 13, 2012 at 14:25

Rufinus

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2 Comments

jjmontes Over a year ago

Shuffle won't return repeated values.

Rufinus Over a year ago

i know, but to be honest it wasnt part of the question. the real question would be "how to generate hex colors randomly" anyway, to which @Timur gave the correct answer.

jprofitt · Accepted Answer · 2012-01-13 14:22:47Z

2

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));

answered Jan 13, 2012 at 14:22

jprofitt

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3 Comments

jjmontes Over a year ago

Shuffle won't return repeated values.

jprofitt Over a year ago

@jjmontes Excellent point, but neither will array_rand() which is what he was initially using, nor did he say it was a requirement

jjmontes Over a year ago

Indeed. Thanks for taking the time to explain that.

Umbrella · Accepted Answer · 2012-01-13 14:29:34Z

2

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.

answered Jan 13, 2012 at 14:29

Umbrella

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1 Comment

jjmontes Over a year ago

Note that there is no guarantee that this method has the same probability for every colour.

jjmontes · Accepted Answer · 2012-01-13 15:31:44Z

1

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);

edited Jan 13, 2012 at 15:31

answered Jan 13, 2012 at 14:30

jjmontes

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3 Comments

Timur Over a year ago

php.net/manual/en/function.array-rand.php - as of PHP 4.2.0, The random number generator is seeded automatically.

jjmontes Over a year ago

Thanks Timur, updating the answer as per your comment.

jprofitt Over a year ago

array_shuffle() isn't a function. shuffle(), however, is.

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