Re: Replace elements in a matrix

*To*: mathgroup at smc.vnet.net*Subject*: [mg116447] Re: Replace elements in a matrix*From*: Daniel Lichtblau <danl at wolfram.com>*Date*: Wed, 16 Feb 2011 04:32:36 -0500 (EST)

kiz_0987 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. > Among other methods: val = 1; stencil = Unitize[a-val]; stencil*a + (1-stencil)*b Out[10]= {{0, 3}, {2, 2}} Daniel Lichtblau Wolfram Research