Re: Using Select
- To: mathgroup at smc.vnet.net
- Subject: [mg97414] Re: Using Select
- From: "Karsten W." <Karsten.G.Weinert at googlemail.com>
- Date: Thu, 12 Mar 2009 05:44:20 -0500 (EST)
- References: <gpacsh$ms3$1@smc.vnet.net>
Ok, this one I can answer myself, now that I have learned about Pick[] data = Import[...]; dataEval = f[data, ...]; filterQ = Map[# > 0&, dataEval]; filteredData = Pick[data, filterQ]; Looks much better to me. Best wishes, Karsten. On 12 Mrz., 08:16, "Karsten W." <Karsten.G.Wein... at googlemail.com> wrote: > Hello, > > here is a problem I have solved but I am not happy with the method > > I have a data matrix DATA, a list of m ordered n-tuples. I run a > function on the data matrix which returns a list DATAEVAL with m > elements. The i-th element of this list corresponds to the i-th tuple > of the data matrix. I think of this DATAEVAL list as an additional > column of the data matrix. > > Now I am only interested in those tuples of the data matrix, where the > corresponding DATAEVAL list has a value greater than zero. > > My current approach is the following: I add the DATAEVAL list to the > data matrix and call Select afterwards: > > data = Import[...]; > dataEval = f[data, ...]; > filteredData = Select[Transpose[Join[Transpose[data], {dataEval}] ], > Last[#] > 0 &]; > > This works. However, calling Transpose two times seems not to be the > most efficient way to solve the problem. > > As a newbie to Mathematica (and functional programming), I wonder if > you can point me to a simpler solution? > > Kind regards, > Karsten.