Random Numbers (Yet Unique)

abelajohnb

Hello.

I am attempting to generate different random numbers and needing to ensure that the same random number does not appear twice.

I have, for example:

$foo1 = "";
$foo2 = "";
$foo3 = "";
$foo4 = "";
$foo5 = "";

Each $foo value would always need to be unique and each instance must always be between: 1 and 13

i.e. :

$foo1 = "6";
$foo2 = "3";
$foo3 = "12";
$foo4 = "9";
$foo5 = "11";

Anybody have any clue as to how to code that?

Thanks.
Jba

brandonschnell

how bout:

1) creating a 13 element array with the values 1-13

2) randomize the order of the elements in the array

3) loop through the elements in the new order to get unique random numbers.

abelajohnb

How does this look?

srand ((double)microtime()*1000000);
$some_array = range(1,13);
shuffle($some_array);
for ($i = 1; $i <= 5; $i++) {
print $some_array[$i];
echo " ";
}

I know it works, but what are the chances of a duplication?

Thanks.

brandonschnell

with a range of 13, there is a very good chance of duplication.

another method would be to pick a random number, if its in an array of numbers thats already been used then pick another number. otherwise add the new random number to the array so that its not used.

jc94062

Two ways.

One, if its sorted in a db compare the new random number to that stored, same, get another, different, add it.

Two, just generate the list.
Well, save the random number to a variable like, using the code JbA gave us...

<?php
srand ((double)microtime()1000000);
$foo1 = range(1,13);
shuffle($some_array);
for ($i = 1; $i <= 5; $i++) {
print $foo1[$i];
echo " ";
}
srand ((double)microtime()1000000);
$foo2 = range(1,13);
shuffle($some_array);
for ($i = 1; $i <= 5; $i++) {
print $foo2[$i];
echo " ";
}
if $foo2 == '$foo1' {unset $foo2; srand ((double)microtime()*1000000);
$foo2 = range(1,13);
shuffle($some_array);
for ($i = 1; $i <= 5; $i++) {
print $foo2[$i];
echo " ";
}
}
?>

Something like that should work, I'm a bit rusty on some of the unset stuff and I'm almost positive it can be done via a while loop, not sure how atm though.

Hope that helps in some form, I gotta sleep.

kparker

How can there be any chance of duplication, since he creates an array
containing 1 .. 13, shuffles it, then outputs only the first 5 elements?
Or do you mean between separate runs of the code? Of course there
could be duplication between runs, since we're not maintaining state here.

Back to the original question: we are all aware, I hope, that if you ask
for random numbers and then put additional stipulations on them, you
are increasing the predictability, and thus reducing the randomness?
Perhaps a hint of why this is needed would help us point in a more
useful direction?

Anon

How should they be duplicated??

Your're picking the first 5 elements of an array, that has exactly 13 different (meaning unique) values.

By shuffeling, they still remain unique, and by picking 5 elements (of that shuffeled array) they are still unique, for shuffle() doesn't duplicate, as we all know!

There certainly is a chance of each $fooX variable having the same value, with the chance of about 1:370 000

Have I got you completly wrong??

Tom

Anon

sorry, haven't read your answer before posting mine, guess, we agree 😉

Tom

brandonschnell

yah, the range() & shuffle() method should work and return unique values. looks like i misread jbA's 2nd post =)

another issue is that shuffle doesn't seem to be very random with some versions of php. if he always pulls the first 5 values after a shuffle the results may look similiar every time. anyone else have a similiar problem? maybe its time to upgrade php again...

abelajohnb

Hello Guys.

Thanks for all the comments/suggestions.

I think I have it (in fact I do).
I did, as suggested, have to go with an array, instead.

Here is what I came up with:

<?php
srand ((double)microtime()*1000000);
$randomnumber = range(1, 13);
shuffle($randomnumber);
for ($i = 1; $i <= 5; $i++) {
print $randomnumber[$i]." ";
}
?>

And, for the newbies 🙂

<?php
$NumQuanity = "5"; //- Quantity of Numbers To Print
$MinNumber = "1"; //- Lowest Random Number To Generate
$MaxNumber = "13"; //- Highest Random Number To Generate
srand ((double)microtime()*1000000);
$randomnumber = range($MinNumber,$MaxNumber);
shuffle($randomnumber);
for ($i = 1; $i <= $NumQuanity; $i++) {
print $randomnumber[$i]." ";
}
?>

Thanks, everyone, for posting your thoughts, suggestions, and comments!

JbA