MATLAB: How to swap this matrix

Question

i have this column of matrix

Z= 2

   4
   1
   7
   9
how to swap this 1 and 2

Answer 1

Z([1,2]) = Z([2,1]);

ADD

Z = [2
   4
   2
   1
   7
   9
   1
   1]; % new case
a = [1, 2]; % replacement value
[l,ii] = ismember(Z,a);
Z(l) = a(3-ii(l));