Re: easy question about random numbers

*To*: mathgroup at smc.vnet.net*Subject*: [mg53399] Re: easy question about random numbers*From*: Justin Kaeser <jast-news at zno.de>*Date*: Sun, 9 Jan 2005 23:04:02 -0500 (EST)*References*: <crqb7f$cak$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Pedrito wrote: > For instance: > If we need to simulate an unfair dice, we could have this probabilities > for each one of the sides: > {1/6, 1/6, 1/6, 1/6, 9/60, 11/60} > > So I wrote: > li2 = {1/6, 1/6, 1/6, 1/6, 9/60, 11/60} > li3=FoldList[Plus,0,li2] > Module[{i = 1, r = Random[]}, While[ !li3[[i]] < r < li3[[i + 1]], i++]; i] > > It works ok but I don't know if there is another (better) way of doing > this. > Any suggestion? I came up with this, which basically implements your idea in a different style: DiscreteRandomFunction[p_List] := Module[{intervals = FoldList[Plus, 0, p], r}, (r = Random[]; Length[Select[intervals, # â?¤ r &]] - 1) &] This creates a function which returns random numbers with the given distribution p. Usage: drf = DiscreteRandomFunction[{1/6, 1/6, 1/6, 1/6, 9/60, 11/60}] to get the function drf[] to get the numbers It appears to be marginally faster than your version (ca 2% ;) but still by magnitudes slower than Random[]. I'd love to see a more effeicent algorithm.