Sorting element pairs by differences?

Question

Marco Bakker 2016-10-7

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https://ww2.mathworks.cn/matlabcentral/answers/306219-sorting-element-pairs-by-differences

评论： Jos (10584) 2016-10-7

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]

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Answer 1

uu tsi 2016-10-7

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https://ww2.mathworks.cn/matlabcentral/answers/306219-sorting-element-pairs-by-differences#answer_237946

在 MATLAB Online 中打开

the following is my code

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

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Jos (10584) 2016-10-7

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).

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Answer 2

Massimo Zanetti 2016-10-7

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

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Answer 3

Jos (10584) 2016-10-7

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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.