Re: Using Select within Map
- To: mathgroup at smc.vnet.net
- Subject: [mg71794] Re: Using Select within Map
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Wed, 29 Nov 2006 02:56:36 -0500 (EST)
- Organization: Uni Leipzig
- References: <ekh70s$s7p$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
Hi,
a) the parser will parse if correct as to see from
Hold[Map[Select[#, a < #[[1]] < b &], x]] // FullForm
b) if you use
Map[Select[#, Function[{q},a < q[[1]] < b],x]
you will not mix up the two Slot[]s
Regards
Jens
Mark Teagarden wrote:
> Hi,
>
> I have a data set which comprises several paired lists, like so (I apologize
> if the tabs do not come out correctly in your mail client):
>
> x =
> {
> {
> { , },
> { , },
> { , }
> },
> {
> { , },
> { , },
> { , }
> },
> {
> { , },
> { , },
> { , }
> }
> }
>
> What I would like to do is to select from each of those paired lists, only
> those pairs where the first value in the pair falls within some specified
> range, and then obtain a mean. This would be simple enough if I was
> operating on a single paired list, for example:
>
> Select[x[[1]],a < #[[1]] < b&]
>
> However, I would like to Map over x so that I would end up with means for
> each of the level 1 lists within x; therein lies the problem. Both Map and
> Select use the Slot operator (#), and I don't know how to distinguish
> between the slot operator used by Map, and the slot operator used by Select:
>
> Select[#,a < #[[1]] < b&]/@x
>
> Or if you prefer:
>
> Map[Select[#, a < #[[1]] < b&,x]
>
> This problem has been plaguing me for some time, and if I could punch
> through it I would be very happy indeed. Any ideas? I have had no luck
> looking through the archives or the Help Browser. On a similar note, I
> would eventually like to modify this solution so that the criteria, a and b,
> could vary with each level 1 list in x, but one thing at a time...
>
> Thanks in advance,
> Mark
>