Re: easy question about random numbers
- To: mathgroup at smc.vnet.net
- Subject: [mg53387] Re: easy question about random numbers
- From: "Ray Koopman" <koopman at sfu.ca>
- Date: Sun, 9 Jan 2005 23:03:37 -0500 (EST)
- References: <crqb7f$cak$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Pedrito wrote: > Hi everybody! > > I wanted to obtain a discrete random number generator that I needed for > a project. > > On the library Statistics`DiscreteDistributions` I could find the DiscreteUniformDistribution > function. But I wanted to specify the probability for each one of the > states. > > > 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? If, as in your example, all the probabilities in li2 are ratios of exact integers, then first get li3 = Flatten@MapIndexed[Table[#2,{#1}]&,li2*LCM@@(1/li2)]; n = Length@li3 Then li3[[Random[Integer,{1,n}]]] will return a random integer from the probability distribution in li2.