Matlab, comparing array using if statement

Question

I have searched the net trying to find an answer to this problem I have.

I have an array much like the following

A = [2 4 6 8 ; 3 5 7 9 ; 1 4 6 9]

r         


        

Answer 1

Here's how I would do that:

MedianMap = ...
    ( bsxfun(@gt,A,col_median) & bsxfun(@gt,A,row_median.') ) - ...
    ( bsxfun(@lt,A,col_median) & bsxfun(@lt,A,row_median.') );

This one is multi-threaded (suited for much larger problems) and doesn't have any of the temporaries involved in the other answers (much smaller peak memory footprint).

It's not very pretty though :) So if better readability is what you're after, use either meshgrid as in BrianL's answer, or repmat:

Col_median = repmat(col_median, size(A,1),1);
Row_median = repmat(row_median.', 1, size(A,2));

MedianMap = ...
    ( A > Col_median & A > Row_median ) - ... 
    ( A < Col_median & A < Row_median ); 

or multiplication by a ones-matrix as Rasman did:

Col_median = ones(size(A,1),1) * col_median;
Row_median = row_median.' * ones(1,size(A,2));

MedianMap = ...
    ( A > Col_median & A > Row_median ) - ... 
    ( A < Col_median & A < Row_median );