Sorting element pairs by differences?

Suppose values is a vector, how to produce a matrix whose rows contain pairs of elements of this vector, ordered ascending by the differences between the elements.

For example:

    values = [1,2,1.5,1.9]

I want the matrix

    differences = [1.9 2; 1.5 1.9; 1 1.5; 1.5 2; 1 1.9; 1 2]

Answer 1

[uu tsi]

the following is my code

 values = [1,2,1.5,1.9];
 ss = nchoosek(values, 2);
 [~, idx] = sort(abs(diff(ss')));
 res = ss(idx, :)

[Jos (10584)]

Thanks for having put my answer in code. As a follow-up: diff(A,1,2) is faster than diff(A'), and A.' (transpose)is more versatile than A' (conjugate transpose).

Answer 2

[Massimo Zanetti]

More elegant is to use pdist, that does the bad job..

Answer 3

[Jos (10584)]

Take a look at NCHOOSEK, ABS, DIFF, and SORT:

• with X = nchoosek(values,2) you can get all the 6 different combinations
• use Y = abs(diff(X)) to get the absolute differences
• the second output of the function sort, applied tot these latter values, can be uses to sort the combinations accordingly.