Re: Elegant syntax for multiple conditional assignment?
- To: mathgroup at smc.vnet.net
- Subject: [mg54424] Re: Elegant syntax for multiple conditional assignment?
- From: Scott Hemphill <hemphill at hemphills.net>
- Date: Sun, 20 Feb 2005 00:09:35 -0500 (EST)
- References: <cv6q9a$65c$1@smc.vnet.net>
- Reply-to: hemphill at alumni.caltech.edu
- Sender: owner-wri-mathgroup at wolfram.com
Scott Hemphill <hemphill at hemphills.net> writes:
> 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.
Maybe I should have given a more concrete example:
old = {Array[olda,{5}], Array[oldc,{5}], Array[oldx,{5}], Array[oldy,{5}]};
new = {Array[newa,{5}], Array[newc,{5}], Array[newx,{5}], Array[newy,{5}]};
cond = {True,False,True,False,True};
I want to assign:
a = {newa[1], olda[2], newa[3], olda[4], newa[5]}
based on the conditions in cond, and similarly for c, x, and y.
Scott
--
Scott Hemphill hemphill at alumni.caltech.edu
"This isn't flying. This is falling, with style." -- Buzz Lightyear