collect rows of a matrix having a desired number in the first row

If I have a matrix, what is the fastest way to collect the columns which satisfy a logical operation in the first row?

So if I have the matrix

 0 5 3 6 4 5 8 4 7 5 1
 5 6 7 5 6 7 8 9 4 5 2
 3 4 3 5 8 3 5 4 4 5 1
 9 6 7 1 6 3 7 4 5 3 8
 9 2 9 5 0 4 2 5 6 3 4

if I wanted to collect all rows which have a 5 in the first row I would have

 5 5 5
 6 7 5
 4 3 5
 6 3 3
 2 4 3

It is important that it is as fast as possible.

Answer 1

[Azzi Abdelmalek]

A=[0 5 3 6 4 5 8 4 7 5 1
5 6 7 5 6 7 8 9 4 5 2
3 4 3 5 8 3 5 4 4 5 1
9 6 7 1 6 3 7 4 5 3 8
9 2 9 5 0 4 2 5 6 3 4]
B=A(:,A(1,:)==5)

[Christopher]

Sorry I made a mistake. How, instead, do I get the following index from the original matrix:

 0 1 0 0 0 1 0 0 0 1 0
 0 1 0 0 0 1 0 0 0 1 0
 0 1 0 0 0 1 0 0 0 1 0
 0 1 0 0 0 1 0 0 0 1 0
 0 1 0 0 0 1 0 0 0 1 0

[Azzi Abdelmalek]

repmat(A(1,:)==5,size(A,1),1)