MATLAB Answers

Sort Index - Bug

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Rainer Ng
Rainer Ng on 19 Sep 2019
Commented: Rainer Ng on 19 Sep 2019
[a, sort_index]=sort([100;20;30;40])
The sort_index should return
4
1
2
3
But it does not.

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Accepted Answer

Walter Roberson
Walter Roberson on 19 Sep 2019
>> [a, sort_index]=sort([100;20;30;40])
a =
20
30
40
100
sort_index =
2
3
4
1
This output is correct. It tells you that a(1) == 20 came from element #2 of the input, and that a(2) == 30 came from element 3 in the input, and that a(3) == 40 came from element 4 of the input, and that a(4) == 100 came from element 1 of the input.
To get the output you want, use
b(sort_index) = 1:length(sort_index);

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More Answers (1)

James Tursa
James Tursa on 19 Sep 2019
The sort index gives the location in the original array of the sorted values. I.e., the sort results "a" are "original_array(sort_index)"
>> x = [100;20;30;40];
>> [a,sort_index] = sort(x)
a =
20
30
40
100
sort_index =
2
3
4
1
>> x(sort_index)
ans =
20
30
40
100
>> isequal(x(sort_index),a)
ans =
1

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Rainer Ng
Rainer Ng on 19 Sep 2019
I apologize. I should have understood this. Thank you.

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