[R] union of two sets are smaller than one set?

[Martin Møller Skarbiniks Pedersen]

This is really puzzling me and when I try to make a small example
everything works like expected.

The problem:

I got these two large vectors of strings.

> str(s1)
 chr [1:766608] "0.dk" ...
> str(s2)
 chr [1:59387] "043.dk" "0606.dk" "0618.dk" "0888.dk" "0iq.dk" "0it.dk" ...

And I need to create the union-set of s1 and s2.
I expect the size of the union-set to be between 766608 and 766608+59387.
However it is 681193 which is less that number of elements in s1!

> length(base::union(s1, s2))
[1] 681193

Any hints?

Regards
Martin

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