Re: rand random. You've got to be kidding

Ruby
1

In a message dated 11/28/2006 11:08:19 A.M. US Mountain Standard Tim,
[email protected] writes:

Surely it must be possible to initialize rand with current date and time.
Documents seem to indicate this is done with rand(0) or srand with no
value. I
have tried both methods and I get the same tired old sequence of numbers. I
would write my own random number generator except I don’t know how to get a
numeric value out of Time.

Can you post the code that isn’t working for you?

I was running the following in SciTE
class Dominoes
attr_writer :deck
def initialize(number)
@deck= Array.new
0.upto(number) {|i| 0.upto(i) {|j| @deck.push([i, j])}}
end

def shuffle!
@deck = @deck.sort{rand}
p @deck
end
end

a=Dominoes.new(6)
a.shuffle!

The p @deck was added so I could see what was being done.

Every time I press F5 I get exactly the same result:
[[6, 6], [4, 4], [0, 0], [5, 0], [1, 1], …
I get the same results if I wait a few minutes or come back the next
day. I
get exactly the same results when I use fxri and freeRIDE. I am running
Ruby
version 1.18.4.

Charlie

2

On Nov 28, 2006, at 1046 , [email protected] wrote:

how to get a
numeric value out of Time.

Can you post the code that isn’t working for you?

Please quote your replies correctly.

I was running the following in SciTE
class Dominoes
attr_writer :deck
def initialize(number)
@deck= Array.new
0.upto(number) {|i| 0.upto(i) {|j| @deck.push([i, j])}}
end

def shuffle!
@deck = @deck.sort{rand}

You want @deck = @deck.sort_by { rand }

[[6, 6], [4, 4], [0, 0], [5, 0], [1, 1], …
I get the same results if I wait a few minutes or come back the
next day. I
get exactly the same results when I use fxri and freeRIDE. I am
running Ruby
version 1.18.4.

Try:

10.times do puts rand end

then:

srand Time.now.to_i

10.times do puts rand end

–
Eric H. - [email protected] - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant

http://trackmap.robotcoop.com

3

Your problem is with
@deck.sort{rand}

------------------------------------------------------------- Array#sort
array.sort -> an_array
array.sort {| a,b | block } -> an_array

 Returns a new array created by sorting _self_. Comparisons for the
 sort will be done using the +<=>+ operator or using an optional
 code block. The block implements a comparison between _a_ and _b_,
 returning -1, 0, or +1. See also +Enumerable#sort_by+.

    a = [ "d", "a", "e", "c", "b" ]
    a.sort                    #=> ["a", "b", "c", "d", "e"]
    a.sort {|x,y| y <=> x }   #=> ["e", "d", "c", "b", "a"]

rand produces always produces values between 0 and 1 so it will always
sort the same :slight_smile:

so you need something like this

@deck.sort { if rand < 0.5 then -1; else 1; end }

Ken