Re: Get list of function variables?

*To*: mathgroup at smc.vnet.net*Subject*: [mg83425] Re: Get list of function variables?*From*: Jason Quinn <jason.lee.quinn at gmail.com>*Date*: Tue, 20 Nov 2007 03:49:53 -0500 (EST)*References*: <fhjs5v$4t3$1@smc.vnet.net>

On Nov 16, 5:42 am, Jason Quinn <jason.lee.qu... at gmail.com> wrote: > This seems simple but how do I get the arguments to an arbitraryfunction? Ideally something like getVariables[f] that just accepts thefunctionname as its argument. > > If I have f[x_,y_]:=a*x^2+b*y^2, getVariables[f] should return {x,y} > If I have g[n_,m_]:=a*n^2+b*m^2, getVariables[g] should return {n,m} > If I have h[w_,x_,y_,z_]:=A*w*x*y*z+B, getVariables[h] should return > {w,x,y,z} Thanks everybody for your responses and help. I made two complete solutions out of the help that was offered. getVariables1[function_] := (Map[ReleaseHold, Apply[List, DownValues[function][[All, 1]], {2}]] /. p_Pattern :> First[p])[[1]] getVariables2[function_] := Union[First /@ Cases[DownValues[function], HoldPattern[Verbatim[HoldPattern][function[z__]]] :> z, Infinity]] Both do what I required of them. The bottom solution does not always preserve the order of the variables in its output but it appears the top one does. I wouldn't have ever figured these out because I had no idea about DownValues (and still don't quite get it even after reading the Mathematica book.) I'm going to try to tackle the inverse problem: making a function out of a list of variables. Not sure yet, but I'm guessing UpValues might have something to do with it. Jason