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Re: Replace elements in a matrix

  • To: mathgroup at smc.vnet.net
  • Subject: [mg116476] Re: Replace elements in a matrix
  • From: Mala Jozsef <mala_jozsef at freemail.hu>
  • Date: Wed, 16 Feb 2011 04:37:50 -0500 (EST)

kiz_0987 <kp.0987 at gmail.com> =EDrta:
>I&#39;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.
>
Hi, the simple way of doing it may be this: c1=Table[If[a[[i,j]]==1,b[[i,j]],a[[i,j]]],{i,m},{j,n}] or c2=Sign[a-1]^2*(a-b)+b hth, Jozsef


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