Question

This seems like a simple question but I have been unable to find an answer anywhere. If I have a Matlab matrix A consisting of an arbitrary number of rows, how would I filter these rows based on the value of some function f (the argument of which is a row vector)? In other words, how would I keep only the rows of matrix A for which f is true? I tried

A(f(A(:)), :)

but to no success. Any help would be greatly appreciated.

Answer 1

As Dan answered, you can filter the rows of a matrix according to a logical vector. Let selectRows be a logical vector with numel(selectRows) == size(A,1) with true for rows to be kept, and false for rows to be discarded. Then:

A( ~selectRows, : ) = [];

Will remove all rows for which selectRows == false.

Now, the question is how to generate the logical vector selectRows using the function f?

If f knows how to process multiple rows, and return multiple true/false values accordingly, then

selectRows = f(A);

Should do the trick.

However, if f only knows how to process one row at a time you will need to loop through the rows. One way of doing so would be

selectRows = cellfun( @f, mat2cell( A, ones(size(A,1)), size(A,2) ) );