How to remove zeros from an array????

I have a array as

a=1:20

 Columns 1 through 15

     1     2     3     4     5     6     7     8     9    10    11    12    13    14    15

Columns 16 through 20

    16    17    18    19    20

and another array as

y =

     1     2     3    13    15    16    17    19    20

then i want to find the elements of y which are not in a so

 b=~ismember(a,y);
b1=bsxfun(@times,a,b)

b1 =

Columns 1 through 15

     0     0     0     4     5     6     7     8     9    10    11    12     0    14     0

Columns 16 through 20

     0     0    18     0     0

now i want to remove the 0's finally i want a matrix x

x=

4 5 6 7 8 9 10 11 12 14 18

please help me...

thank you

Answer 1

[Stephen23]

Simply use logical indexing directly on a (those b variables are not required):

>> a(~ismember(a,y))
ans =
    4    5    6    7    8    9   10   11   12   14   18

or the simplest solution is to use setdiff:

>> setdiff(a,y)
ans =
    4    5    6    7    8    9   10   11   12   14   18