The output result of intersect function is not as the expected one

For example, when I run the following codes:

   Cell1 = {'C';'B';'ZN';'FU';'PM';'A';'OI';'SR';'M';'TA';'AU';'P';'RU';'CU';'Y';'L';'AL';'CF';'WH'};
   Cell2 = {'B';'ZN';'FU';'PM'};
  [~,Index] = intersect(Cell1,Cell2);

The expected value of Index should be [2,3,4,5] However, when I run codes in MATLAB2014b,the results I have got is [2,4,5,3].

But, when I replace Cell1 and Cell2 as:

Cell1 = {'A','B','C','D'};
Cell2 = {'A','B'};
[~,Index] = intersect(Cell1,Cell2);

I got Index = [1,2],which is the same as the expected value.

So, weird. Hope someone can tell me what the cause of this problem.

Answer 1

[Guillaume]

By default, intersect sorts its output, and thus the indices returned correspond to that sorted order. You would have seen that had you asked for the intersection:

>>Cell1 = {'C';'B';'ZN';'FU';'PM';'A';'OI';'SR';'M';'TA';'AU';'P';'RU';'CU';'Y';'L';'AL';'CF';'WH'};
>>Cell2 = {'B';'ZN';'FU';'PM'};
>>[intersection ,Index] = intersect(Cell1,Cell2)
intersection = 
  'B'
  'FU'
  'PM'
  'ZN'
Index =
   2
   4
   5
   3

If you want to keep the output in the same order as your first array, then use the stable option:

>>[intersection ,Index] = intersect(Cell1, Cell2, 'stable')
intersection = 
  'B'
  'ZN'
  'FU'
  'PM'
Index =
   2
   3
   4
   5

[Xie Ya]

Thanks very much. Now I got it.