Xapian devel - Mar 2014 - Regarding implementation of Evalmetric class in Letor

Hi Parth,

I've implemented SVMRanker class
here<https://github.com/mayank193/xapian/tree/xapian-letor> in
this branch. And it works same as original non-refactored code(at least for
the random queries for which I have tried). Now coming back to implement
Evalmetric class, I am facing the problem where to start? Though I've
implemented MAP and NDCG vaguely
here<https://github.com/mayank193/xapian/blob/xapian-letor/xapian-letor/evalmetric.cc>,
I haven't tested them. The reason being I am not able to follow up the
structure in the Ranker and EvalMetric classes.

1. What is the structure that has to followed in EvalMetric class? Will it
serve as a base class class for MAP and NDCG sub-classes or will something
like
this<https://github.com/mayank193/xapian/blob/xapian-letor/xapian-letor/evalmetric.h>will
do?

2. In Ranker.h, don't you think that functions for getting MAP and NDCG
scores should be defined? Why two objects for Evalmetric are defined
here<https://github.com/mayank193/xapian/blob/xapian-letor/xapian-letor/ranker.h#L50>?
Also the functions for setting validata and testdata data members?

It would certainly help if you could give me an overview how Evalmetric
class interacts with other classes.

Thanks

Mayank
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