Filtering the Content of an Array

Suppose I have an array, arr with contents as follow:

        A       B       C       D
        1  3  2  3
        1  4  1  2
        1  3  3  5
        2  6  1  4
        2  5  4  3
        2  6  3  3
        2  4  3  2
        2  5  4  2
        4  2  4  4
        4  1  4  6
        4  6  5  3
        71  1  4  4
        71  3  2  3
        71  3  1  1
        71  4  1  3
        71  3  2  3
        71  5  2  2

How can I filter the results to achieve the following:

        A  B  C  D
        2  6  1  4
        2  5  4  3
        2  6  3  3
        2  4  3  2
        2  5  4  2
        71  1  4  4
        71  3  2  3
        71  3  1  1
        71  4  1  3
        71  3  2  3
        71  5  2  2

[Jan]

There is an infinite number of possible solutions. Although we can try to use our crystal balls, this could be a source of missunderstandings. Please explain the wanted procedure with any details.

Please note, that the type and size of the "arrays" is not clear: Does "A,B,C,D" belong to the array, such that it must be a cell arrays, because numerical arrays cannot contain numbers and characters? Or ist this any kind of header, and the actual data are 4 vectors or 1 matrix?

The less we have to guess, the easier and more likely helpful is the answer.

Answer 1

[Andrei Bobrov]

ABCD = [1  3  2  3        
        1  4  1  2        
        1  3  3  5        
        2  6  1  4        
        2  5  4  3        
        2  6  3  3        
        2  4  3  2        
        2  5  4  2       
        4  2  4  4 
        4  1  4  6 
        4  6  5  3 
        71  1  4  4
        71  3  2  3
        71  3  1  1
        71  4  1  3
        71  3  2  3
        71  5  2  2];

out = ABCD(ABCD(:,1) == 2 | ABCD(:,1) == 71,:);

or

out = ABCD(ismember(ABCD(:,1),[2 ,71]),:);