Re: Using Select within Map

*To*: mathgroup at smc.vnet.net*Subject*: [mg71799] Re: Using Select within Map*From*: dh <dh at metrohm.ch>*Date*: Wed, 29 Nov 2006 02:56:49 -0500 (EST)*Organization*: hispeed.ch*References*: <ekh70s$s7p$1@smc.vnet.net>

Hi Mark, Mathematica is clever enough to figure where an argument belongs if this is possible. E.g.: Map[2 # &, Select[{a, b, c, a}, (# == a || # == b) &]] Of course, if you e.g. multiply arguments of different functions, there is no way Mathematica could know which argument belongs to which function. If the # notation does not work, there is still the notation: Function[x,..] that works with named arguments. Daniel 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 >