Replace values in matrix

Hi everybody I have a matrix, for ex: A=[2 5 7 12 9 4] and another matrix B=[1 4]

ı want to replace elements apart from 1. and 4. as "NaN". (2., 3., 5., and 6., element must be equal to NaN) I tried if command, but i took an error. Is there any pratical command for this operation? Thanks.

Answer 1

[Stephen23]

>> A = [2,5,7,12,9,4];
>> B = [1,4];
>> A(~ismember(1:numel(A),B)) = NaN
A =
     2   NaN   NaN    12   NaN   NaN

[Volkan Yangin]

Thank you Mr.Cobeldick.