Hello,

I have a list of historical datas of this form:

Histodata1                      Histodata2              ...     Histodatan
1 Jan 1980 Data1                25 Jan 1980 Data2               2 Jan 1980
Datan
2 Jan                           26 Jan                  3 Jan 1980
...
31 Dec 2004                     29 dec 2004                     1 dec 2004


This is implemented as

class histodata {
public:
 typedef std::vector<entry>::iterator iterator;
private:
 std::vector<entry> data_;
};

I need to obtain the union of all this data without duplicating the
individual datas, so I wrote a

class hisodataset { // contains a unique set of histodatas
 /// this contains the n datas
 /// Define the iterator

};

The requirements of the iterator: bidirectional, but if RanAcc is possible,
it would be good.
. We want the union of datas, so that, if a date is present in at least 1,
then the it should be present in the union. For those histodatas that don't
have the date, it should simply duplicate the last available date for that
histodata.
. begin() on the set will return the earliest date available for all
histodatas
.end () will return the "one-after-last" last being the last date available
in all histodatas.

I'm not quite sure how to implement such an iterator.
boost::zip_iterator over the underlying histodatas, but how to add to that
the union part?

only a const version of this union iterator is required, no writing needed.