Re: Elegant syntax for multiple conditional assignment?
- To: mathgroup at smc.vnet.net
- Subject: [mg54409] Re: [mg54337] Elegant syntax for multiple conditional assignment?
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Sun, 20 Feb 2005 00:08:18 -0500 (EST)
- Reply-to: hanlonr at cox.net
- Sender: owner-wri-mathgroup at wolfram.com
old={a1,c1,x1,y1}; new={a2,c2,x2,y2}; cond={True,False,True,False}; {a,c,x,y} = If[#[[1]],#[[2]],#[[3]]]&/@ Transpose[{cond,new,old}] {a2,c1,x2,y1} {a,c,x,y} = If[#[[1]],#[[2]],#[[3]]]&/@ Thread[{cond,new,old}] {a2,c1,x2,y1} Bob Hanlon > > From: Scott Hemphill <hemphill at hemphills.net> To: mathgroup at smc.vnet.net > Date: 2005/02/19 Sat AM 02:31:38 EST > To: mathgroup at smc.vnet.net > Subject: [mg54409] [mg54337] Elegant syntax for multiple conditional assignment? > > Dear Mathematica aficionados: > > I have several state variables, each of which is a vector of "n" elements. > I would like to assign each element in each vector based on a condition > which is in the corresponding position in a condition vector. To be more > specific: > > Each of a, c, x and y is a List of Length n. > cond is a List of Length n, containing True and False values > > What I have is > > old = {a, c, x, y}; > > code which changes a, c, x, and y > > new = {a, c, x, y}; > > What I want to do is assign to each element of a, c, x and y the old value > of a, c, x or y if the corresponding element of cond is False, and the new > value of a, c, x or y if the corresponding element of cond is True. > > I've got a method that works: > > t=Transpose; > {a, c, x, y} = t[If[#[[1]],#[[2]],#[[3]]]& /@ t[{cond,t[new],t[old]}]]; > > All the transpositions and array indexing make me wonder if there's a more > elegant way of expressing this. > > Any takers? Thanks in advance. > > Scott > -- > Scott Hemphill hemphill at alumni.caltech.edu > "This isn't flying. This is falling, with style." -- Buzz Lightyear > >