Re: Elegant syntax for multiple conditional assignment?

*To*: mathgroup at smc.vnet.net*Subject*: [mg54416] Re: [mg54337] Elegant syntax for multiple conditional assignment?*From*: DrBob <drbob at bigfoot.com>*Date*: Sun, 20 Feb 2005 00:08:48 -0500 (EST)*References*: <200502190731.CAA05948@smc.vnet.net>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

(inputs) old = Array[o, {4}] new = Array[n, {4}] cond = Array[1 == Random[Integer, {0, 1}] & , {4}] (outputs) {o[1], o[2], o[3], o[4]} {n[1], n[2], n[3], n[4]} {True, False, True, False} (input) Thread[If[cond, Evaluate[new], Evaluate[old]]] (result) {n[1], o[2], n[3], o[4]} or: old = {a, c, x, y} = Array[o, {4}] new = {a, c, x, y} = old^2 cond = Array[1 == Random[Integer, {0, 1}] &, {4}] {o[1], o[2], o[3], o[4]} {o[1]^2, o[2]^2, o[3]^2, o[4]^2} {True, False, False, False} {a, c, x, y} = Thread[If[cond, Evaluate@new, Evaluate@old]] {o[1]^2, o[2], o[3], o[4]} Bobby On Sat, 19 Feb 2005 02:31:38 -0500 (EST), Scott Hemphill <hemphill at hemphills.net> wrote: > 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 -- DrBob at bigfoot.com www.eclecticdreams.net

**References**:**Elegant syntax for multiple conditional assignment?***From:*Scott Hemphill <hemphill@hemphills.net>