Rand(), Srand()

Nickosssss

I have this code....the $key_projs points to ID numbers from a database query the same as the $key_studs....how can i assign random keys to students? The point is that this rand must be from the keys on the array

$keys_projs = array_keys($not_full_projects);
//print_r($test);

$keys_studs = array_keys($unallocatedStuds);
//print_r($t2);

$arraycount = count($keys_projs);

$i=0;
while($i < $arraycount)
{
$rest = array($keys_studs[$i] => $keys_projs[$i]);

$unallocatedStuds[$keys_studs[$i]] = srand($keys_projs[$i]);
$not_full_projects[$keys_projs[$i]]--;

toplay

I got to run, but check out this function:

http://us3.php.net/manual/en/function.array-rand.php

hth.

bradgrafelman

So $unallocatedStuds is an array of unused ID's? Simple!

$newID = $unallocatedStuds[rand(0, count($unallocatedStuds))];
echo "Your new ID is: $newID";

Nickosssss

well it is an array of this type

[111] -> 0
[122] -> 0
.....

the [ ] its an id from the database table...(student id number)

bradgrafelman

So it's like...

$theArray = array(111 => 0, 122 => 0);

?? Why in the world would you put it in that format? :p Leaving the format intact, you can do virtually the same thing (same approach), just add a step: take all of the keys of the indices and put them in an array:

$newID = array_keys($unallocatedStuds);
$newID = $newID[rand(0, count($newID))];

Nickosssss

well i am doing an allocation algorithm and i needed to have the id numbers of students pointing to what projects they have taken...if 0 no project has been taken....thats why 🙂

thank you mate i am going to try it

Nickosssss

actually is not really an array but a hash table....but i hope it will work

Nickosssss

mmm....it does not work like i want it....let me show u some of the code so u can understand better

$top = "SELECT * from topic";
$res_top = $db->query($top);

$topics = array();

while ($row_top = $res_top -> fetch_assoc())
{

$topics[$row_top['top_id']] = $row_top['max_stud'];

}

$super = "SELECT * from staff";
$res_staff = $db->query($super);

$staffs = array();

while($row_staff = mysqli_fetch_assoc($res_staff))
{
$staffs[$row_staff['staff_id']] = $row_staff['max_stud_no'];
}

so the topic and staff are not actually arrays but hash tables....and i think thats why rand does no play as supposed to be...

bradgrafelman

But... we're working with $unallocatedStuds though... where do you define that?

Let's make it easy. Do this:

print_r($unallocatedStuds);

and paste the output for me. That way, I can see the structure of that variable.

Nickosssss

the output of that would be like that....i didnt want to give lots of details because it can comfuse you...the print_r prints those two "arrays" like that but as u can see.....it does not start from [0],[1],[2] because the [111] is an id number from the SELECT statement. The same happens with the students

PROJECTS

[111] => 1

[112] => 1
[113] => 2
[114] => 3
[115] => 2
[116] => 1
[117] => 1
[118] => 1
[119] => 3
[120] => 2
[121] => 1
[122] => 2
[123] => 3
[124] => 1
[125] => 2
[128] => 2
[129] => 1
[130] => 1

STUDENTS

[1111111] => 0
[1212121] => 0
[1313131] => 0
[1414141] => 0
[1515151] => 0
[1616161] => 0
[2222222] => 0
[2888555] => 0

toplay

Nickosssss, you seemed to have ignored or not seen my first post here. The function array_rand() will return a random key from your array. It will work even if your keys don't start from zero on.

I still don't really understand what you're trying to do with the array. But MySQL can do a lot of things for you (so you don't have to do it all with just PHP). If you want to retrieve one random row from lets say the topic table, then do:

$top = "SELECT * from topic ORDER BY RAND() LIMIT 1";
$res_top = $db->query($top);
$row_top = $res_top->fetch_assoc();

That way you don't have to read all the rows. If what you want is just to get a random row, then that's what I recommend that you use.

🙂

Nickosssss

i did try what u said toplay but didnt work and i didnt know why....i cant use RAND in the SELECT because i have an algorithm which allocates projects to students....those who are not allocated then they allocated from the rest of the projects! And this process needs to be random assignment.....i ll try again thanks

bradgrafelman

The only reason I didn't post exactly what toplay suggested is because he had already posted it. That would have been my first method of choice.

Try implementing his approach one more time, and if it still doesn't work, give us some sample output turn on display_errors and set it to "E_ALL" so we know what's going on) and the relevant section of code you tried.