The Code to replace non-threshold indexes in Array

Hello,

A = randi(5,5);

idx = find(A > 3);

A(idx) = log10(A(idx));

After running the above lines of code, what's the easiest(fastest) way to replace the non idx index in A with a certain value(100 for example)?

A(~idx) = 100; doesn't work the way I intended to.

Thanks!

Answer 1

[Steven Lord]

Get rid of the find call.

A = randi(5,5)

A = 5×5

5 3 2 2 5 1 1 4 5 3 1 4 2 5 2 1 2 3 2 2 1 1 2 5 3

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idx = (A > 3) % Make a logical mask

idx = 5x5 logical array
   1   0   0   0   1
   0   0   1   1   0
   0   1   0   1   0
   0   0   0   0   0
   0   0   0   1   0

A(idx) = log10(A(idx)) % Use the logical mask to identify locations to change

A = 5×5

0.6990 3.0000 2.0000 2.0000 0.6990 1.0000 1.0000 0.6021 0.6990 3.0000 1.0000 0.6021 2.0000 0.6990 2.0000 1.0000 2.0000 3.0000 2.0000 2.0000 1.0000 1.0000 2.0000 0.6990 3.0000

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A(~idx) = 100 % Use the negation of the logical mask to identify locations to change

A = 5×5

0.6990 100.0000 100.0000 100.0000 0.6990 100.0000 100.0000 0.6021 0.6990 100.0000 100.0000 0.6021 100.0000 0.6990 100.0000 100.0000 100.0000 100.0000 100.0000 100.0000 100.0000 100.0000 100.0000 0.6990 100.0000

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