Remove all values of 3 from array

a = [1 2 3 4 3];
a(any(a==3,1)) = []
a =
     1     2     4

Remove 2 or less from array

a = [1 2 3 4 3];
a(any(a<=2,1)) = []
a =
     3     4     3

Remove values between 2 and 3

a = [1 2 3 4 3];
a(any((a>=2)&(a<=3),1)) = []
a =
     1     4

Based on examples from matlabnewbie.

Remove values (12 & 13) based on a set (array):

a = 11:20;
a = setdiff(a,[12,13])
a = 
    11    14    15    16    17    18    19    20