I have a 2D matrix (81,000,000 x 2). Each row has a radius value and an intensity value. The radii are not in a monotonic in this 2D matrix. I want to sort 1st column from min to max and have column 2 move with it.

I have a 9000 x 9000 matrix containing a radial distribution of energy from the center out. I want to plot Value vs. Radius. to fine R= 0 I look for the X,Y position of the maximum pixel,(X0,Y0). Then I go through the matrix and calculate the radius value for each pixel with R = sqrt((X-X0)^2 + (Y - Y0)^2). I store the Radius value and the intensity of that pixel in a two column matrix with Radius in Column 1, value in column 2. How do I sort radius values from min to max and have the associated column #2 go along with the sort? My (npts,2) matrix is about (81,000,000 x 2). I need to sort column 1 in ascending order but can't figure out how to make sure the value in column 2 move along with the sort so it is still associated with that radius value. Can you help?

Answer 1

[Matt J]

newmatrix=sortrows(oldmatrix,1);

[Paul Manhart]

Thanks. It works. The definition in sortrows did not say anything about carrying the 2nd column with it. So I assumed it was left alone.

[Matt J]

You're welcome, but please Accept-click an answer that solved your issue.

[dpb]

The name is the hint (vs just sort) and the description says "B = sortrows(A) sorts the rows of a matrix in ascending order based on the elements in the first column."

Answer 2

[dpb]

doc sortrows

Or, of course, you can do it yourself via

[~,ix]=sort(A(:,1));    % return index to sorted position of first column
A=A(ix,:);              % reorder A by row in sorted order given by ix

[Paul Manhart]

Thanks dpb