FAQ Topic - How do I generate a random integer from 1 to N? (2008-09-03)

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FAQ Topic - How do I generate a random integer from 1 to
N?
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Method Math.random() returns a value R such that 0 <= R < 1.0 ; therefore

function Random(x) { return Math.floor(x*Math.random()) }

gives an evenly distributed random integer in the range from 0 to
x-1 inclusive; use ` Random(N)+1 ` for 1 to N.

http://msdn2.microsoft.com/en-us/library/41336409.aspx

http://docs.sun.com/source/816-6408-10/math.htm

How to Deal and Shuffle, see in:

http://www.merlyn.demon.co.uk/js-randm.htm


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re: FAQ Topic - How do I generate a random integer from 1 to N? (2008-09-03)

FAQ server wrote:Excuse me, Mr/Mrs FAQ server, is that really correct? When
I try e.g. x = 1.5, do I really get evenly distributed results?

Errare humanum est. I hope I made an error: then I learned
something.

re: FAQ Topic - How do I generate a random integer from 1 to N? (2008-09-03)

The argument, x, must be a positive integer.

If you want a real number between 0 and 1.5 then use x=1.5 but don't use
the floor function.

Good point.

re: FAQ Topic - How do I generate a random integer from 1 to N? (2008-09-03)

In comp.lang.javascript message <48be132f$0$23607$f4da826c@news.24online
..fi>, Wed, 3 Sep 2008 07:31:39, optimistx <optimistxPoista@poistahotmail
..composted:ISTR that a previous FAQ maintainer was told that the argument of Random
was intended to be integer, but did not act on that (ICBW).

He also wanted to put a lower limit of 2 on x !

"therefore" should be replaced by "therefore, with positive integer x,".

However, one can use the function with other arguments, if you find it
useful.


The Microsoft and Sun references do not explicitly say that the number
is evenly distributed (I believe its evenness in imperfect in IE).

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