hi,
i have an array @number = [1,2,3,4,5,6,7,8,9]
now, i want to randomize the array content... something like eg: [5,3,2,6,7,1,8]
please guide me how to proceed with it.
thanks
A:
loop n times
i = random array index
j = random array index
swap elements i and j
end
RyanHennig
2010-09-29 04:41:11
Random is not guaranteed to give properly distributed results. Therefore, swapping elements with two random indexes might give you array with blocks of unchanged sequences in the middle. You should increment i from 0 to n and take random j to ensure *all* elements get swapped at least once.
gaearon
2010-09-29 04:45:58
Awful. Even and odd `n` gives two different sets of permutations. It's so sad, but still some teachers teach students of this method... Never do that!
Nakilon
2010-09-29 04:54:41
@Nakilon: What are you talking about? Why does it matter if n is even or odd?
RyanHennig
2010-09-29 17:37:18
@RyanHennig. 1. If you give me original `array` and `n`, I should tell you, what half of permutations' set you can't get, and what you can. With `[1,2,3,4,5]` and `n%2 == 1` you'll never get `[5,4,3,2,1]`. 2. Also, in ideal random suffled array statistically the `1` element is in its _original_ (where it would be in oredered array) place. Your shuffling of array with `1mln` elements will take at least `7mln` swappings to make array with `2` element on their _original_ places.
Nakilon
2010-09-30 06:59:04
@gaearon: There was no requirement to ensure that all elements get swapped at least once.
RyanHennig
2010-10-15 03:51:12
@Nakilon: 1. Of course you can. Swap 1 and 5, 2 and 4, and then 3 with itself. 2. I don't know what you mean by this point
RyanHennig
2010-10-15 03:54:24
@RyanHennig, hm, sorry, I didn't think about swapping with itself.
Nakilon
2010-10-15 09:20:50
+3
A:
Use the shuffle method ...
irb(main):001:0> [1,2,3,4,5].shuffle
=> [3, 4, 2, 5, 1]
Dave Pirotte
2010-09-29 04:42:57
+7
A:
the shuffle command returns a randomized version of an array
eg:
[1,2,3].shuffle => [2,3,1]
Nikolaus Gradwohl
2010-09-29 04:43:10
and if you want to randomize in place, you can just write `@number.shuffle!`
Peter
2010-09-29 05:08:36
A:
If you are using old version of ruby... this will work
def randomize(array)
b = []
array.length.downto(1) { |n|
b.push array.delete_at(rand(n))
}
b
end
a = [1,2,3,4,5] b=randomize(a) print b
Avinasha
2010-09-29 05:01:35