How can I only keep keys that have the smallest value pair in a matrix?

I'm trying to create an edge detection program that creates a matrix with coordinates of just the surface of whatever subject we're examining. After using the canny edge detection filter I have all the coordinates of what the filter is calling the surface, which includes multiple rows within the same column. I'm trying to create a new matrix such that only the smallest row number numbers are assigned to each column.

For instance, If I have an n x 2 array like

A = [1 10; 1 15; 1 20; 2 35; 2 46; 2 57;] 

I would want an output that looks like

B = [1 10; 2 35]

Answer 1

[Walter Roberson]

[g, val] = findgroups(A(:,1));
B = [val, accumarray(g, A(:,2), [], @min)];