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From: Chris Russell (cdr_at_[hidden])
Date: 2003-08-31 06:17:36

Hello folks, I've got an interesting little design problem and I'm looking
for some advice on how best to implement an efficient solution.

[ I posted this message to comp.lang.c++.moderated yesterday. I'm reposting
here because this _seems_ like a job for some type of iterator adaptor and
I'm thinking that perhaps one of the Boost libraries might be useful in this
context. But which (if any)? Would uBLAS help me here perhaps? Or am I way
off base? ]

Here's a simplified statement of the problem that I believe outlines the
relevant details:

I've got a class declared as follows:

--- begin example class ----
class CFilter
typedef struct tag_sRow
A_t A;
B_t B;
C_t C;
.. // some number of structure members...
} sRow_t;

typedef std::map<key_t/*type unimportant*/, sDataRow_t> mapData_t;
typedef mapDataSet_t::iterator mapiterData_t;
typedef mapDataSet_t::const_iterator mapconstiterData_t;

mapData_t m_mapData;


void ProcessRow(const sRow_t& sRow)
// process a single row of data
} // end method ProcessRow

void ProcessData(const mapData_t& mapData)
// algorithm needs fast access to:
// std::vector<A_t>, std::vector<B_t>, std::vector<C_t> ....
} // end method ProcessData

}; // end class declaration CFilter

--- end example class ---

In English: CFilter declares some structure with some number of data members
of arbitrary types. Internally CFilter allocates a std::map of these
structures using some key_t. Effectively this defines a table of data whose
rows are of type sRow_t, and whose columns can be conceptualized as
std::vector<A_t>, std::vector<B_t> where
std::vector<sRow_t.some_member>.size() == mapData<key_t, sDataRow_t>.size().

At runtime, CFilter.ProcessRow is called std::map<key_t, sRow_t>.size()
times followed by a single call to CFilter.ProcessData.

I'm trying to figure out how to _efficiently_ access the column vectors in
the implementation of CFilter.ProcessData.

Any suggestions would be greatly appreciated.

Thanks in advance - Chris Russell

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