HOW-TO produce random numbers within a range?

ruby-talk
1

Hello,
Thanks for reading this.
I am very new to Ruby and have been learning using a tutorial at
http://pine.fm/LearnToProgram/
by Chris (thanks Chris)
After searching fairly thoroughly in forums and tutorials I found no
answer to my problem.
I have come to a point where i need to generate a random number within a
range.

I have learnt that rand(100) produces random numbers from 0 to 99 but i
need to know how to set a minimum for the random number.

Your help would be greatly appreciated.

Thanks in advance, tckl.

···

--
Posted via http://www.ruby-forum.com/.

2

Just add the minimum value to whatever number you generate. For example, if
you wanted to generate a random number between 0 and 99 with a minimum value
of 20:

rand(80) + 20

···

On 1/6/07, Ruby N00bie <ralphallan@gmail.com> wrote:

I have learnt that rand(100) produces random numbers from 0 to 99 but i
need to know how to set a minimum for the random number.

Your help would be greatly appreciated.

Thanks in advance, tckl.

--

3

Suppose the range is 50-99.

Generate a random number between 0 and 50, and add 50 to the result.

m.

···

Ruby N00bie <ralphallan@gmail.com> wrote:

Hello,
Thanks for reading this.
I am very new to Ruby and have been learning using a tutorial at
Learn to Program, by Chris Pine
by Chris (thanks Chris)
After searching fairly thoroughly in forums and tutorials I found no
answer to my problem.
I have come to a point where i need to generate a random number within a
range.

I have learnt that rand(100) produces random numbers from 0 to 99 but i
need to know how to set a minimum for the random number.

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4

<...>

I have learnt that rand(100) produces random numbers from 0 to 99 but i
need to know how to set a minimum for the random number.

Your help would be greatly appreciated.

<...>

Add the minimum :slight_smile:

def range_rand(min,max)
  min + rand(max-min)
end

···

--
Regards,
Rimantas
--
http://rimantas.com/

5

Welcome abord !

Easier to make it fit it that fit your self.
The Ultimate Morphing Lego Game.

#!/usr/bin/my_new_lego_game

alias old_rand rand

def rand(min,max)
  until min < r=old_rand(max); end
  return r
end

10.times do |x|
    p rand(1,10)
end

-.rb

···

--
Posted via http://www.ruby-forum.com/.

6

Ruby N00bie wrote:

Hello,
Thanks for reading this.
I am very new to Ruby and have been learning using a tutorial at
Learn to Program, by Chris Pine
by Chris (thanks Chris)
After searching fairly thoroughly in forums and tutorials I found no
answer to my problem.
I have come to a point where i need to generate a random number within a
range.

I have learnt that rand(100) produces random numbers from 0 to 99 but i
need to know how to set a minimum for the random number.

Your help would be greatly appreciated.

Thanks in advance, tckl.

--
Posted via http://www.ruby-forum.com/\.

You don't need to be able to set a minimum. You simply take what
rand() gives you and add an offset.

25.times{ r = rand(10); print "#{ r } " }

5 1 0 5 4 3 5 0 4 0 7 8 6 8 6 9 7 1 7 9 9 3 5 7 5 => 25

25.times{ r = rand(10); print "#{ r + 50 } " }

57 51 51 58 54 53 56 58 54 57 54 56 57 58 50 56 56 50 58 52 58 55 53 50
56 => 25

7

You have to do this yourself, say you want a random number between 42 and a
than you have to write

42+rand(a+1-42) # BTW it would be legal to write a - 41 :wink:
It would be nice an exercise to define your own method to do this

HTH
Robert

···

On 1/6/07, Ruby N00bie <ralphallan@gmail.com> wrote:

Hello,
Thanks for reading this.
I am very new to Ruby and have been learning using a tutorial at
Learn to Program, by Chris Pine
by Chris (thanks Chris)
After searching fairly thoroughly in forums and tutorials I found no
answer to my problem.
I have come to a point where i need to generate a random number within a
range.

I have learnt that rand(100) produces random numbers from 0 to 99 but i
need to know how to set a minimum for the random number.

Your help would be greatly appreciated.

Thanks in advance, tckl.

--
Posted via http://www.ruby-forum.com/\.

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incomplete ideas."

- Alan Kay

8

Thanks very much all three of you.
That's all I needed to know.
tckl

···

--
Posted via http://www.ruby-forum.com/.

9

Don't do this. It is *really* inefficient. Compare these...

10.times do |x|
     p rand(10000000,10000005) # Your new slow rand
end

10.times do |x|
  p rand(5) + 10000000 # old rand
end

···

On 7/01/2007, at 8:02 AM, Rodrigo Bermejo wrote:

def rand(min,max)
  until min < r=old_rand(max); end
  return r
end