randomise array via key

[ozonew4m]

hello guys and gals

lets say i have 100 values in the array..

what i want to do is provide a key to randomly generate an array of 50 values from the 100

the key needs to generate exactly the same values every time from the array (so i guess its not really random)

so if i give the key value of say 12345

it will generate the same 50 from the 100 every time..

i thought about using md5 in combination with shuffle but im not sure how to do it completely

any guidance please

[Andrewaclt]

Why not check to see if the key has been used before, if so grab results from db. Otherwise randomly grab 50 values and write them to a database/flatfile corresponding to the key.

[php_daemon]

I tend to agree with Andrew, it's a simple way. You can use array_rand to pull the random values, assign a key and store to db. Next time you use the same key, fetch the data from database.

[byron3@earthlink]

Random numbers generated by the rand() function are pseudo-random.
You have the ability to seed the rand() function using srand().
I have not tested this but if you use the same seed integer for rand() then you should get the same output.

The following contain documentation on both functions.
http://us.php.net/rand
http://us.php.net/manual/en/function.srand.php

[ozonew4m]

im not using a database its just an array

[kromey]

As per byron's suggestion, then, seed rand (well, actually, you should mt_rand instead as it is faster and more, well, random - seed it with mt_srand). Then generate 50 array keys with mt_rand(0,99) and pull those corresponding array values out; if you seed with the same number, you'll always get the same output.

[stereofrog]

hello guys and gals

lets say i have 100 values in the array..

what i want to do is provide a key to randomly generate an array of 50 values from the 100

the key needs to generate exactly the same values every time from the array (so i guess its not really random)

so if i give the key value of say 12345

it will generate the same 50 from the 100 every time..

i thought about using md5 in combination with shuffle but im not sure how to do it completely

any guidance please

For example:

function random_subarray($ary, $len, $key) {
    srand($key);
    shuffle($ary);
    return array_slice($ary, 0, $len);
}

# example
$chars = range('a', 'z');
print_r(random_subarray($chars, 5, 123)); 

same $key value generates same selection every time.

hope this helps.

[ozonew4m]

peeeeeeeerfect stereofrog

Thank you all for your input