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Re: Replace elements in a matrix
*To*: mathgroup at smc.vnet.net
*Subject*: [mg116468] Re: Replace elements in a matrix
*From*: Bill Rowe <readnews at sbcglobal.net>
*Date*: Wed, 16 Feb 2011 04:36:23 -0500 (EST)
On 2/15/11 at 6:32 AM, kp.0987 at gmail.com (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?
Here is one way
In[19]:= b + Unitize[a - 1] (a - b)
Out[19]= {{0, 3}, {2, 2}}
Unitize makes all non-zero entries 1. So, in each position where
a is 1, the expression above becomes b + 0 = b and for each
position where a is not 1 it becomes
b + (a -b) = a
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