Matlab,alphabetic order of the intersect result

Question

I use intersect function to find common strings in two cell arrays A and B ([~,idx]=intersect(A,B))and save indexes in idx. Then I extract the common strings by A(idx). I see that the results are sorted in alphabetic order. I want to sort them as they sorted in A, Why these strings sorted in alphabetic order?

Thanks.

Answer 1

As explained in the documentation, you can add the option setOrder='stable' to preserve the order of the elements:

[C,ia,ib] = intersect(A,B,'stable');

You don't even have to capture the indices (unless used elsewhere), as the example shows:

C = intersect([7 0 5],[7 1 5],'stable')
returns
C = [7 5]

and

A='hgfedcba';
B='hac';
[~,ia]=intersect(A,B,'stable');
ia'

>   1   6   8

A(ia)

>   hca

For Matlab R2011b and older:

If your matlab version doesn't support the 'stable' option, you can just use sort on the indices:

[~,ia]=intersect(A,B);
ia=sort(ia);
A(ia)

>   1   6   8

A(sort(ia))

Duplicates

If they're duplicates in A, intersect will only find them once. ismember might be better suited if you want to find all of the duplicates:

A='hhggffeeddccbbaa';
B='hac';
[~,ia]=intersect(A,B);
ia=sort(ia);
A(ia)

>   hca

[~,loc] = ismember(A,B);
ia=find(loc~=0); % because you want the indices (logical indexing is also an option of course)
A(ia)

>   hhccaa