Re: Replace elements in a matrix

*To*: mathgroup at smc.vnet.net*Subject*: [mg116451] Re: Replace elements in a matrix*From*: DrMajorBob <btreat1 at austin.rr.com>*Date*: Wed, 16 Feb 2011 04:33:20 -0500 (EST)

a = {{0, 1}, {1, 2}}; b = {{1, 3}, {2, 5}}; c = {{0, 3}, {2, 2}}; c == With[{u = Unitize[a - 1]}, a u + b (1 - u)] True or d = a; p = Position[a, 1] c == ReplacePart[a, Thread[p -> Extract[b, p]]] True Bobby On Tue, 15 Feb 2011 05:32:51 -0600, kiz_0987 <kp.0987 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. > -- DrMajorBob at yahoo.com