Re: shuffling (randomizing) a series

*To*: mathgroup at smc.vnet.net*Subject*: [mg52905] Re: [mg52857] shuffling (randomizing) a series*From*: Daniel Lichtblau <danl at wolfram.com>*Date*: Thu, 16 Dec 2004 03:40:56 -0500 (EST)*References*: <200412150926.EAA10600@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

George Szpiro wrote: > Hello, > > I would like to put a series of numbers (of the order of 10^7 numbers) into > random order, i.e., to shuffle it. In Excel I would simply add a column next > to the column with the data, and then sort by the random number. But I could > only do this for 64000 numbers. How can I do that in Mathematica for a file with a > much larger series? > > (could you please copy any answer to my address: > george at netvision.net.il) > > Thanks! > George This comes up from time to time. One can do it in Mathematica using the method you describe. Another method is shown in a MathGroup note at: http://forums.wolfram.com/mathgroup/archive/2001/Jan/msg00087.html I believe both of these are in the DiscreteMath`Combinatorica add-on package. Here is a faster version of the one in that MathGroup note, suitable for shuffling the entire set (the code in the note was for "dealing" a subset of shuffled elements). This is taken from a notebook in our infocenter repository. http://library.wolfram.com/infocenter/Conferences/325/ shuffleC = Compile[{{n, _Integer}}, Module[{res = Range[n], tmp, rand}, Do[ rand = Random[Integer, {j, n}]; tmp = res[[j]]; res[[j]] = res[[rand]]; res[[rand]] = tmp, {j, 1, n}]; res ]]; For example: len = 10^7; set = Table[Random[], {len}]; Timing[shuffledset = set[[shuffleC[len]]];] Out[17]= {16. Second, Null} Daniel Lichtblau Wolfram Research

**References**:**shuffling (randomizing) a series***From:*George Szpiro <george@netvision.net.il>