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 is how I would do it:

1. Create logical indices for each condition (element greater/less than row/col median)
2. Use the logical indices to update MedianMap.

In code:

[xMedian, yMedian] = meshgrid(col_median, row_median);

isRowHigh = (A > yMedian);
isColHigh = (A > xMedian);

isRowLow = (A < yMedian);
isColLow = (A < xMedian);

MedianMap(isRowHigh & isColHigh) = 1;
MedianMap(isRowLow & isColLow) = -1;

Notes:

• meshgrid expands row_median and col_median into arrays of the same size as A
• A > yMedian returns a matrix of the same size as A containing the boolean results of comparing every element of A with the corresponding element of xMedian.
• isRowHigh & isColHigh performs an element-wise AND of the boolean matrices
• MedianMap(L), where L is a logical index (boolean matrix), selects the elements of MedianMap corresponding to the elements of L which are true.