Re: Replace elements in a matrix

*To*: mathgroup at smc.vnet.net*Subject*: [mg116483] Re: Replace elements in a matrix*From*: Ray Koopman <koopman at sfu.ca>*Date*: Wed, 16 Feb 2011 06:45:23 -0500 (EST)*References*: <ijdo8r$f7a$1@smc.vnet.net>

On Feb 15, 3:32 am, kiz_0987 <kp.0... at gmail.com> wrote: > I'm new to Mathematica and have a question regarding matrices. I was > sure that this problem must have been answered in the past, but could > not find a solution. > > I want to replace some elements in a matrix (based on value) with > elements from another matrix at the same position. Eg: > a = {{0, 1}, {1, 2}}; > b = {{1, 3}, {2, 5}}; > > I want to replace the elements in "a" which are equal to 1 (say) with > the same position elements in b to give: > c = {{0, 3}, {2, 2}}; > > How can I do this? I started with using Position and ReplacePart but > could not figure out how to get it to work in this case (other cases > are documented, such as replacing with a single value). > > Any help appreciated. Thanks. I'm surprised no one suggested this: a = {{0, 1}, {1, 2}}; b = {{1, 3}, {2, 5}}; c = MapThread[If[#1 == 1, #2, #1] &, {a, b}, 2] {{0, 3}, {2, 2}}