Help with Select[]
- To: mathgroup at smc.vnet.net
- Subject: [mg34631] Help with Select[]
- From: "Kevin Gross" <kc144_nospam at ameritech.net>
- Date: Thu, 30 May 2002 02:55:15 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Hello all,
I've got data sets that resemble
setA={
{{x1,0},{x2,0}},
{{x3,0},{x4,0}},
{{x5,1},{x6,0}},
{{x7,1},{x8,1}}
};
setB={
{{x1,0},{x2,0},{x3,0}},
{{x4,0},{x5,0},{x6,0}},
{{x7,1},{x8,0},{x9,1}},
{{x10,1},{x11,1},{x12,0}}
};
Each element of the set is a list of n (x,y) ordered pairs. So n=2 for the
first set and n=3 for the second set. In general, n will differ between the
data sets, but can be known. With each set, I want to select those elements
whose sub-elements all have y=0. This is hard to explain in English, but
easy to express in Mathematica:
In: Select[setA,(#[[1,2]]==#[[2,2]]==0)&]
Out: {{{x1,0},{x2,0}},{{x3,0},{x4,0}}}
In: Select[setB,(#[[1,2]]==#[[2,2]]==#[[3,2]]==0)&]
Out: {{{x1,0},{x2,0},{x3,0}},{{x4,0},{x5,0},{x6,0}}}
First, I would like to know how to generate an arbitrary "selection
function" f[n] so that
In: Select[setC,f[8]]
Out: {{{x1,0},...,{x8,0}},{{x9,0},...,{x16,0}},...}
Is it possible to construct such an f? Or is there a better way of
accomplishing this task? It seems that perhaps pattern matching might be of
use, but I haven't gotten too far with it.
Thanks in advance,
Kevin Gross