Re: listing user defined, independent variables
- To: mathgroup at smc.vnet.net
- Subject: [mg96819] Re: listing user defined, independent variables
- From: Albert Retey <awnl at gmx-topmail.de>
- Date: Wed, 25 Feb 2009 04:07:25 -0500 (EST)
- References: <go0j0p$mta$1@smc.vnet.net>
Paul Ellsmore wrote: > Hi, > > > > I have a notebook in which there are over 1300 variables (symbols) defined. > The vast majority of these are dependent variables. I can get a list of them > all with Names["Global`*"], but what I really want is a list of only the > independent variables. Is there any obvious way to do this? Mathematica must > "know" which variables are functions of other symbols, so I was hoping that > there would be an "attribute" of a dependent variable that I could use as a > filter on Names[]. Any thoughts? I am using V5.1. I don't think that there is an attribute for that information. The internals of mathematica are mostly rule based, and OwnValues[] will give you the information which can be used to determine the dependencies that you are seeking. I could only think about a rather involved way to extract that information, since you need to be careful to not evaluate too early. The following is an approach to determine the dependencies: (*ensure that we can see the symbols, not only the values:*) SetAttributes[dependentQ, HoldFirst] (* if we get a symbol which has an OwnValue, extract the unevaluated RHS of its OwnValue and see whether it contains symbols from the Global context: *) dependentQ[var_Symbol] := If[TrueQ[Length[OwnValues[var]] > 0], Not[FreeQ[Extract[OwnValues[var], {1, 2}, Hold], s_Symbol /; Context[s] == "Global`"]], False ] (* as a filter for variable names, it is handy if we accept strings as arguments, too: *) dependentQ[name_String] := dependentQ @@ ToExpression[name, InputForm, Hold] (* use as filter: *) Select[Names["Global`*"], dependentQ] It might well be that there are simpler and/or more efficient ways to do this, but I can't think of one now and it should be a starting point... hth, albert
- Follow-Ups:
- Re: Re: listing user defined, independent variables
- From: "Paul Ellsmore" <paul.ellsmore@nanion.co.uk>
- Re: Re: listing user defined, independent variables