create binary 0 and 1

Dear all, 
I have matrix of binary with n=5
      A=[0 0 0 0 1
       0 0 0 1 0
       0 0 1 0 0
        ....
       1 1 1 1 1]
  but I only want to take a submatrix with 3 number 1 inside

       subA=[ 0 1 1 0 1
              1 0 1 0 1
              0 1 1 1 0
               ........]
    and 
    subB=[0 0 0 0 1
          0 0 0 1 0
          0 0 1 0 0
          0 1 0 0 0
          1 0 0 0 0
          0 0 0 1 1 
          .....
          0 1 1 0 1
          1 0 1 0 1
          0 1 1 1 0
           ........]
  . Couyld you help me? Thanks

Answer 1

[James Tursa]

subA = A(sum(A,2)==3,:);

For subB it is not entirely clear to me what you want. Do you want the rows of A arranged so that all rows with one 1 come first, then all rows with two 1's, then all rows with three 1's? Or what? E.g., this?

subB = [A(sum(A,2)==1,:);...
        A(sum(A,2)==2,:);...
        A(sum(A,2)==3,:);...
        A(sum(A,2)==4,:);...
        A(sum(A,2)==5,:)];

[Quynh tran]

in subB, I want with 5 colums but number of 1 in a row is less than 3

[James Tursa]

Your words do not match your example. Maybe a truncated version of the above?

subB = [A(sum(A,2)==1,:);...
        A(sum(A,2)==2,:);...
        A(sum(A,2)==3,:)];

or

subB = [A(sum(A,2)==1,:);...
        A(sum(A,2)==2,:)];