Question

in a column, value 2 replace with 1 and value 1 & 3 replace with 2. The code i wrote below got problem:

S=[1 1 1 2 2 3 3 3 3];
S(S==2)=1; S(S==1)=2; S(S==3)=2;

result:

S=[2 2 2 2 2 2 2 2 2]

However, the result i wan to get is S=[2 2 2 1 1 2 2 2 2]. does anyone can help?

Answer 1

That is happening because when in the S(S==1)=2; step, you are affected by the modifications from the S(S==2)=1; step. Try this

S = [1 1 1 2 2 3 3 3 3];
S_copy = S;
S(S_copy == 2) = 1; S(S_copy == 1) = 2; S(S_copy == 3) = 2;

or you could also save the results of the tests into separate variables:

S = [1 1 1 2 2 3 3 3 3];
f1 = (S == 2);
f2 = (S == 1);
f3 = (S == 3);
S(f1) = 1; S(f2) = 2; S(f3) = 2;