Sort Index - Bug

6 vues (au cours des 30 derniers jours)
Rainer Ng
Rainer Ng le 19 Sep 2019
Commenté : Walter Roberson le 14 Avr 2021
[a, sort_index]=sort([100;20;30;40])
The sort_index should return
4
1
2
3
But it does not.

Réponse acceptée

Walter Roberson
Walter Roberson le 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);
  4 commentaires
Franziska Höppe
Franziska Höppe le 13 Avr 2021
Thank you for you detailed answer! :-)
The issue is if you let run the loop, you get a different result. You get:
2
5
2
Do you know why?
Walter Roberson
Walter Roberson le 14 Avr 2021
I never got that output; which code were you using, and which MATLAB version?

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Plus de réponses (1)

James Tursa
James Tursa le 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
  1 commentaire
Rainer Ng
Rainer Ng le 19 Sep 2019
I apologize. I should have understood this. Thank you.

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