remove duplicates from list *preserving order*

[John Machin]

Francis Girard wrote:
> Hi,
>
> I think your last solution is not good unless your "list" is sorted
(in which
> case the solution is trivial) since you certainly do have to see all
the
> elements in the list before deciding that a given element is not a
duplicate.
> You have to exhaust the iteratable before yielding anything.

Last solution? All of them have essentially the same logic to decide
which items to reject.

Further, what you say is true only if you are interpreting Steven's
ambiguous(?) requirement as: remove ALL instances of a bunch of
duplicates. Such a requirement would seem to be (a) just a tad unlikely
and (b) contrary to the output of solutions already shown, which have
brought no protest from Steven.

So, just to remove ambiguity, WHICH one of the bunch should be
retained? Short answer: "the first seen" is what the proverbial "man in
the street" would expect -- "Have you voted already today?" -- it's a
practical requirement and doesn't need any more complicated data
structure than a set of folk who've already voted and no
sleeve-rolling-up.