Re: Help with Select[]
- To: mathgroup at smc.vnet.net
- Subject: [mg34674] Re: Help with Select[]
- From: "Carl K. Woll" <carlw at u.washington.edu>
- Date: Fri, 31 May 2002 04:27:27 -0400 (EDT)
- Organization: University of Washington
- References: <ad4j0u$jkt$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Kevin,
Here is one way (there are many possibilities):
Cases[setB, {{_,0}..}]
Carl Woll
Physics Dept
U of Washington
"Kevin Gross" <kc144_nospam at ameritech.net> wrote in message
news:ad4j0u$jkt$1 at smc.vnet.net...
> 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
>
>