How to replace all but one value with zero

I have generated the following vector f:

f=[49; 18; 48]

And I want to be able to replace each element, except let's say f21, with a value, let's say zero.

f=[0; 18; 0]

I have been playing around with loops, but I cant seem to figure it out just yet..

Does anyone have any advice on how to handle this? Preferably a solution that also works for larger matrices.

Best

Answer 1

[KSSV]

f=[49; 18; 48] ;
f(f~=18) = 0 ;  % repalce by value 

f=[49; 18; 48]
iwant = zeros(size(f)) ;
iwant(3) = f(3) ;  % replace by index 

[Hylke Dijkstra]

Thanks!