# Generating unique random numbers

I’m trying to generate 8 unique random numbers between 1 and 13.

for example my first set of results could be:

2, 8, 4, 6, 3, 10, 12, 1

the results need to be between 1 and 13 and they must be unique.

The rand(12) + 1 returns random numbers between 1 and 13, but they are
not unique. Any quick solutions?

Jimmy P. wrote:

I’m trying to generate 8 unique random numbers between 1 and 13.

for example my first set of results could be:

2, 8, 4, 6, 3, 10, 12, 1

the results need to be between 1 and 13 and they must be unique.

The rand(12) + 1 returns random numbers between 1 and 13, but they are
not unique. Any quick solutions?

~\$ irb
irb(main):001:0> (1…13).to_a.sort_by{rand}[0…7]
=> [7, 3, 8, 2, 11, 4, 1, 9]
irb(main):002:0>

ar = []
while ar.length < 8
ar << rand(12) + 1
ar.uniq!
end

/Shawn

On Mon, Mar 24, 2008 at 6:00 PM, Jimmy P. [email protected]

Tim H. wrote:

~\$ irb
irb(main):001:0> (1…13).to_a.sort_by{rand}[0…7]
=> [7, 3, 8, 2, 11, 4, 1, 9]
irb(main):002:0>

thanks Tim. i like it.

On Mar 24, 7:00 pm, Jimmy P. [email protected] wrote:

Posted viahttp://www.ruby-forum.com/.

Here’s one more possibility:

numbers = (1…13).to_a
randoms = []
8.times {randoms << numbers.delete_at(rand(numbers.size))}

Though, Tim’s solution might be most readable.

Chris

On Tue, Mar 25, 2008 at 10:26 AM, Tim H. [email protected]
wrote:

Jimmy P. wrote:

Tim H. wrote:

~\$ irb
irb(main):001:0> (1…13).to_a.sort_by{rand}[0…7]
=> [7, 3, 8, 2, 11, 4, 1, 9]
irb(main):002:0>

thanks Tim. i like it.

You’re welcome. Turns out you don’t need the to_a. One less method.

(1…13).sort_by{ rand }.first(7)

my attempt to improve upon it

Jimmy P. wrote:

Tim H. wrote:

~\$ irb
irb(main):001:0> (1…13).to_a.sort_by{rand}[0…7]
=> [7, 3, 8, 2, 11, 4, 1, 9]
irb(main):002:0>

thanks Tim. i like it.

You’re welcome. Turns out you don’t need the to_a. One less method.

From: Michael F. [mailto:[email protected]]

# (1…13).sort_by{ rand }.first(7)

careful, Mike ^^^^^^^^

On Mon, Mar 24, 2008 at 9:08 PM, Michael F.
[email protected] wrote:

You’re welcome. Turns out you don’t need the to_a. One less method.

(1…13).sort_by{ rand }.first(7)

my attempt to improve upon it

Tim’s shuffle and cut technique seems fishy to me at first, but I like
it. Now I’ll be up nights reading my old probability texts

Todd

On Tue, Mar 25, 2008 at 10:24:54AM +0900, Chris S. wrote:

## not unique. Any quick solutions?

Posted viahttp://www.ruby-forum.com/.

Here’s one more possibility:

numbers = (1…13).to_a
randoms = []
8.times {randoms << numbers.delete_at(rand(numbers.size))}

Though, Tim’s solution might be most readable.

You might also look through the solutions for Ruby Q. #39 (Sampling).

http://rubyquiz.com/quiz39.html

there are couple of other ruby quizes where things like this are touched
on.
You might browse through the archives.

enjoy,

-jeremy

On Tue, Mar 25, 2008 at 11:26 AM, PeÃ±a, Botp [email protected]
wrote:

From: Michael F. [mailto:[email protected]]

# (1…13).sort_by{ rand }.first(7)

careful, Mike ^^^^^^^^

oh, i meant .first(8) ^^;

^ manveru

On Tue, Mar 25, 2008 at 6:54 AM, Subbu [email protected]
wrote:

Hey Tim, I am a bit lost here sort_by accepts a block. But I see
you are just passing it a method.
Look again
Robert

Whereof one cannot speak, thereof one must be silent.
Ludwig Wittgenstein

On Mar 24, 6:05 pm, Tim H. [email protected] wrote:

not unique. Any quick solutions?

~\$ irb
irb(main):001:0> (1…13).to_a.sort_by{rand}[0…7]
=> [7, 3, 8, 2, 11, 4, 1, 9]
irb(main):002:0>

RMagick:http://rmagick.rubyforge.org/
RMagick 2:http://rmagick.rubyforge.org/rmagick2.html

Hey Tim, I am a bit lost here sort_by accepts a block. But I see
you are just passing it a method. How does this work? Does Ruby
convert the return value of the method to a block and then sorts it?
Do you mind explaining it for me? Thanks so much.

Tim H. wrote:

Jimmy P. wrote:

I’m trying to generate 8 unique random numbers …
the results need to be between 1 and 13
and they must be unique.

~\$ irb
irb(main):001:0> (1…13).to_a.sort_by{rand}[0…7]
=> [7, 3, 8, 2, 11, 4, 1, 9]

For anyone still counting :), the following builds on Tim’s approach:

(1…13).to_a.shuffle.first(8)

Array#shuffle is only available in ruby 1.9+ though.

Cheers, lasitha

Jimmy P. wrote:

I’m trying to generate 8 unique random numbers between 1 and 13.

for example my first set of results could be:

2, 8, 4, 6, 3, 10, 12, 1

the results need to be between 1 and 13 and they must be unique.

The rand(12) + 1 returns random numbers between 1 and 13, but they are
not unique. Any quick solutions?

http://realrand.rubyforge.org/

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