Re: Using Select with arrays? (Relative newbie)

*To*: mathgroup at smc.vnet.net*Subject*: [mg54249] Re: Using Select with arrays? (Relative newbie)*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Mon, 14 Feb 2005 21:50:43 -0500 (EST)*Reply-to*: hanlonr at cox.net*Sender*: owner-wri-mathgroup at wolfram.com

data={ {1,1,string1,c,d} , {1,2,string2,c,d} , {1,3,string3,c,d} , {1,4,string4,c,d}, {2,1,string1,c,d}, {2,2,string2,c,d} , {3,1,string3,c,d} , {4,1,string2,c,d}, {4,2,string4,c,d}}; To select by value of first position Select[data,First[#]==1&] {{1, 1, string1, c, d}, {1, 2, string2, c, d}, {1, 3, string3, c, d}, {1, 4, string4, c, d}} To select ALL members of subset with with specified value in first position and maximum value in second position pickMax2[data_, firstVal_] := Module[{t}, Select[ t=Select[data,First[#]==firstVal&], #[[2]]==Max[t[[All,2]]]&]]; The result is a list of lists since there presumably could be more than one pickMax2[data,1] {{1, 4, string4, c, d}} pickMax2[data,#]& /@ Range[Max[data[[All,1]]]] {{{1, 4, string4, c, d}}, {{2, 2, string2, c, d}}, {{3, 1, string3, c, d}}, {{4, 2, string4, c, d}}} Bob Hanlon > > From: Hugo Mallinson <hfm21 at cam.ac.uk> To: mathgroup at smc.vnet.net > Date: 2005/02/13 Sun PM 10:17:04 EST > To: mathgroup at smc.vnet.net > Subject: [mg54249] Using Select with arrays? (Relative newbie) > > The subject might not be entirely correct, but here is my problem: > > I have a list of 5-variable data points like > > data = { > {1, 1, string1, c, d} > {1, 2, string2, c, d} > {1, 3, string3, c, d} > {1, 4, string4, c, d} > {2, 1, string1, c, d} > {2, 2, string2, c, d} > {3, 1, string3, c, d} > {4, 1, string2, c, d} > {4, 2, string4, c, d} > } > > > and I want to extract just the points that have 1 (or 2, etc) as their > first value. I think I should do something like > > Select[data, {1, _Integer, _String, _Integer, _Integer}] > > but that doesn't work. > > Having done that I need to find the maximum value of #2 for each > string, which I presumably do by the same method as above to extract > all string1 (or ...2) and then use Map[] and Max[]. I would do this all > with For loops (revealing my lack of Mathematica chops :-) ) but I'd > really like to learn how to do this sort of extraction in a > Mathematica-y way. Any help would be greatly appreciated! > > Hugo > >