# Question abour rand()

Discussion in 'Ruby' started by Panagiotis Atmatzidis, Dec 29, 2009.

1. ### Panagiotis AtmatzidisGuest

Dear Sirs,

I'm looking for a way to create a random sequence of numbers using the =
'rand' method. I can think of something like:

-----
while pipi =3D=3D TRUE
if x > 1950 || x < 2000
return x
pipi =3D FALSE
------

Since however the book that I'm reading has not introduced while/else/if =
etc. I'm thinking that there must be an easier and probably more =
sensible way to approach this. As far as I've read rand(2000) will give =
random numbers from 0-to-2000 no matter what.

NOTE: I don't want to use another method just to do the job.

thanks in advance & best regards

Panagiotis (atmosx) Atmatzidis

email:
URL: http://www.convalesco.org
GnuPG ID: 0xFC4E8BB4=20
gpg --keyserver x-hkp://pgp.mit.edu --recv-keys 0xFC4E8BB4
--
The wise man said: "Never argue with an idiot. They bring you down to =
their level and beat you with experience."

Panagiotis Atmatzidis, Dec 29, 2009

2. ### Fleck Jean-JulienGuest

Hello,

> I'm looking for a way to create a random sequence of numbers using the 'r=

and' method. I can think of something like:
>
> -----
> while pipi =3D=3D TRUE
> =A0if x > 1950 || x < 2000

Perhaps you were thinking of "and" rather than "or" because all number
is either greater than 1950 or smaller than 2000.

> Since however the book that I'm reading has not introduced while/else/if =

etc. I'm thinking that there must be an easier and probably more sensible w=
ay to approach this. As far as I've read rand(2000) will give random number=
s from 0-to-2000 no matter what.

Does 'rand(50) + 1950' do what you want ?

Cheers,

--=20
JJ Fleck
PCSI1 Lyc=E9e Kl=E9ber

Fleck Jean-Julien, Dec 29, 2009

3. ### SeebsGuest

On 2009-12-29, Panagiotis Atmatzidis <> wrote:
> while pipi == TRUE
> if x > 1950 || x < 2000
> return x
> pipi = FALSE

Hmm. Looks as though you want the range 1951..1999. Well, that's easy
enough:

rand(49) + 1951

(Note that rand(49) returns anything from 0 to 48, inclusive.)

-s
--
Copyright 2009, all wrongs reversed. Peter Seebach /
http://www.seebs.net/log/ <-- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated!

Seebs, Dec 29, 2009
4. ### Marnen Laibow-KoserGuest

Panagiotis Atmatzidis wrote:
> Dear Sirs,
>
> I'm looking for a way to create a random sequence of numbers using the
> 'rand' method. I can think of something like:
>
> -----
> while pipi == TRUE
> if x > 1950 || x < 2000
> return x
> pipi = FALSE
> ------
>
> Since however the book that I'm reading has not introduced while/else/if
> etc. I'm thinking that there must be an easier and probably more
> sensible way to approach this. As far as I've read rand(2000) will give
> random numbers from 0-to-2000 no matter what

Use Seebs' suggestion.

>
> NOTE: I don't want to use another method just to do the job.

Then you are probably being silly. It will make for more readable and
more reusable code if you encapsulate this in a method. Having lots of
short methods is generally a *good* thing.

>
> thanks in advance & best regards
>
>
>
> Panagiotis (atmosx) Atmatzidis
>
> email:
> URL: http://www.convalesco.org
> GnuPG ID: 0xFC4E8BB4
> gpg --keyserver x-hkp://pgp.mit.edu --recv-keys 0xFC4E8BB4

Best,
--
Marnen Laibow-Koser
http://www.marnen.org

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

Marnen Laibow-Koser, Dec 29, 2009
5. ### Phillip GawlowskiGuest

On 29.12.2009 18:00, Marnen Laibow-Koser wrote:

>> NOTE: I don't want to use another method just to do the job.

>
> Then you are probably being silly. It will make for more readable and
> more reusable code if you encapsulate this in a method. Having lots of
> short methods is generally a *good* thing.

"Walk before you run."

--
Phillip Gawlowski

Phillip Gawlowski, Dec 29, 2009
6. ### Bertram ScharpfGuest

Hi,

Am Dienstag, 29. Dez 2009, 18:51:53 +0900 schrieb Panagiotis Atmatzidis:
> I'm looking for a way to create a random sequence of numbers using the 'rand' method. I can think of something like:
>
> -----
> while pipi == TRUE
> if x > 1950 || x < 2000
> return x
> pipi = FALSE
> ------
>
> Since however the book that I'm reading has not introduced while/else/if etc. I'm thinking that there must be an easier and probably more sensible way to approach this. As far as I've read rand(2000) will give random numbers from 0-to-2000 no matter what.
>
> NOTE: I don't want to use another method just to do the job.
>
> thanks in advance & best regards

The "rand" method has been mentioned. Here are just some

You don't need a loop for calculating a random value. (There is a
random algorithm below.) But when use a loop, then you either say
"return" or leave it by a condition but not both.

cond = true
while cond do
...
if some_condition then
cond = false
end
...
end

_or_

loop do
...
break if some_condition
...
end

Note that "break" can even return values:

result = loop do
break "hi"
end
result == "hi"

And here is an example of a very simple random implementation:

class R
def initialize
@r = 0
end
def nextval
@r = ((@r * 0xabcd) + 0x73737) % 0x1_0000_0000
@r >> 16
end
end
r = R.new
new_random_value = r.iterate
random_value_below_fifty = r.iterate % 50

Bertram

--
Bertram Scharpf
Stuttgart, Deutschland/Germany
*
Discover String#notempty? at <http://raa.ruby-lang.org/project/step>.

Bertram Scharpf, Dec 29, 2009
7. ### Brian CandlerGuest

Panagiotis Atmatzidis wrote:
> I'm looking for a way to create a random sequence of numbers using the
> 'rand' method.

Others have answered the 'random number between 1950 and 2000' bit.

In terms of creating a "sequence" of these values, here are a couple of
options to consider.

(1) Build an array.

a = []
10.times { a << rand(50) }

This array (a) is an object which can be returned, passed to other
functions etc. The above code hard-codes the number of values to build
(10), but you could choose this dynamically at run-time instead.

(2) Yield the values.

For code which wants to "return" multiple values, you can instead
"yield" the values to a block which the caller provides. You can yield
multiple times, thus calling the block multiple times. In other
programming languages you might call this a "callback function"

def generate_random(n=10)
n.times do
yield rand(50)
end
end

generate_random do |r|
puts "I got #{r}!"
end

Note that you can legitimately yield an infinite number of times,
because the block can abort the sequence when it wants. So in the
following example, the user of the function decides when they don't want
any more random numbers:

def generate_infinite
loop do
yield rand(50)
end
end

count = 0
generate_infinite do |r|
puts "I got #{r}!"
count += 1
break unless count < 10
end

A more advanced way to do this is with an 'Enumerator' object, but I'd