Replace elements in a matrix

*To*: mathgroup at smc.vnet.net*Subject*: [mg116428] Replace elements in a matrix*From*: kiz_0987 <kp.0987 at gmail.com>*Date*: Tue, 15 Feb 2011 06:32:51 -0500 (EST)

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.