I have had a look at the Time Series docs and it looks like a worthwhile library, though I have not done anything recently with time-indexed data that could use it. I have, however, had to deal with sparse vs. dense data structure decisions with other index types, e.g. integers; this leads me to wonder what ties this library specifically to _time_ series. One of the elements of this library is a pair of containers that have a common interface but store their contents either in a dense or a sparse structure. I wonder whether it would be worth generalising those containers to make them applicable to non-time applications - and to make them as close to standard library containers as possible. One way to approach this would be to think about how a std::map-like interface can be presented to a std::vector, and/or how a std::vector-like interface can be presented to a std::map. My motivation is that I sometimes find myself with code like this: typedef std::map<int,T> T_container; // I'm not sure yet if this is best stored in a sparse T_container tt; // (map) or dense (vector) structure, but by making // it a typedef I can easily change it later. Of course, when I change the typedef from map<int,T> to vector<T> I discover that there are plenty of other places where I have to change the code; for example I have to add or remove '->second' wherever I dereference an iterator. How about: dense_map<int,T> : provides the interface of std::map<int,T> (or a subset of it), implemented using a vector. Needs to grow the vector when something is inserted. sparse_vector<T> : provides the interface of std::vector<T> (or a subset of it), implemented using a map. Needs an iterator that can point to gaps between the map elements. How close do the sparse and dense time series containers come to this? Regards, Phil.