Re: Selecting Many Things Rather Than Selecting One Thing From Many

*To*: mathgroup at smc.vnet.net*Subject*: [mg66199] Re: [mg66180] Selecting Many Things Rather Than Selecting One Thing From Many*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Thu, 4 May 2006 05:19:46 -0400 (EDT)*Reply-to*: hanlonr at cox.net*Sender*: owner-wri-mathgroup at wolfram.com

m = Table[Random[Integer, 1000], {1000}, {3}]; k = {34, 876, 199}; sel=Select[m, MemberQ[k, #[[1]]]&] {{876, 551, 965}, {34, 454, 475}, {876, 810, 192}} pos = Position[m, _?(MemberQ[k, #[[1]]]&), 1, Heads->False]//Flatten {202, 459, 721} sel == m[[pos]] True Bob Hanlon ---- Gregory Lypny <gregory.lypny at videotron.ca> wrote: > Hello everyone, > > I've discovered another use or need for the Select function, which I > suspect requires mapping of some sort. > > In my previous posts, members of this MathGroup kindly showed me how > to apply Select to many columns of a matrix at once. For example, > > (Select[#1, #1 > K & ] & ) /@ Transpose[theMatrix] > > will pull out all values greater than K, where K is a number such as > 100. > > But suppose now that K is a list of numbers, such as K={34, 876, > 199}, and I simply want to extract or identify all of the rows in the > first column of theMatrix equal to any one of those numbers. How > would I do that? I started with > > Select[theMatrix, #[[1]]==any element of list K] > > and I imagine something similar could be applied to the Position > function. > > Any hint would be much appreciated. > > Gregory >