MATLAB: Undo-sort does not work for large arrays

Question

Hi,

I am trying to undo a sort in this way:

>> a = [1,2,5,4,3];
>> [b,I] = sort(a);
>> isequal(b(I),a)
ans =
       1

But when I try with a larger data set it doesn't work.

>> [ue_seq_sorted, I] = sort(ue_seq);
>> isequal(ue_seq_sorted(I),ue_seq)
ans =
       0
>> whos
  Name               Size                Bytes  Class      Attributes
    I                  1x98635            789080  double                            
    ue_seq             1x98635            789080  double               
    ue_seq_sorted      1x98635            789080  double

The data has much larger integers – for example:

Columns 98633 through 98635
     135673517   135674897   135676277

Is there another way to sort/undo the sort here?

Thank you!

Kind regards, Martin

Answer 1

The shown method does not even work for small arrays. For your examples the matching result is just an exception.

The 2nd output of sort is not the inverse sorting index.

Please try this (I do not have access to Matlab currently):

[ue_seq_sorted, I] = sort(ue_seq);
index(I) = 1:length(ue_seq);