# Replacing all values of a with b in a matrix?

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JARED VAHRENBERG on 29 Oct 2020
Commented: JARED VAHRENBERG on 29 Oct 2020
Say I define that a and b are 3 and 4, respectively. I heva a matrix M that I want to swap all instances of a with b. How would I do that? I tried doing
res = M(M==a) = b;
it works if I don't have the res there but I need the res there to output my result for this specific issue. It keeps telling me it needs to be
res = M(M==a) == b; but that only gives me the 2x1 logical array that has 0 0 in it
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JARED VAHRENBERG on 29 Oct 2020
For example say I wanted to have matrix M= [2,5;2,8] and wanted to swap the 2's out for 1's to where then I get res = [1,5;1,8]. Why is it that my code works in the command window but as soon as I add in that res in the editor it gets angry?

madhan ravi on 29 Oct 2020
What do you expect == is a logical operator, when not used in symbolic calculations if you just want to assign it, then simply use
res = M;
res(res == a) = b
JARED VAHRENBERG on 29 Oct 2020
Ah that worked thanks a lot