[pymvpa] Using FeatureSelectionClassifier for feature elmination
James M. Hughes
james.m.hughes at Dartmouth.EDU
Thu Jul 17 02:04:04 UTC 2008
On Jul 16, 2008, at 16:36 , Yaroslav Halchenko wrote:
> then the rest is easy: feature_selector is a helper which selects
> features for us (discard 20% in current example), and
> update_sensitivity says
> that we would like to reassess sensitivity of rfesvm at each step of
> RFE, since
> otherwise we could simply compute sensitivity with all the features
> and start
> pruning without explicitly retraining classifier for each selected
> subset of
> features to get a new sensitivity (implicitly we still need to
> retrain it
> because we use ConfusionBasedError, thus it would alter while we are
> altering
> subset of the features. update_sensitivity = False is specific if we
> use
> sensitivity_analyzer which is not classifier based, ie smth like
> Anova.
so when we call clf.train(dataset_1) where clf is a SplitClassifier,
it selects features and trains several classifiers using the splits?
When we then call clf.predict(dataset_test.samples), it uses only
those features selected during training? (This is sort of the point
of confusion for me -- i.e., when we call 'predict' on the trained
classifier, that it uses the selected features). Probably this is
really obvious, but I just want to be 100% sure about this.
Thanks for the email -- generally it cleared up almost all of my
questions. I'd be happy to write up the docs for RFE based on what
you wrote, once I get a better hang of using the package.
Cheers,
James.
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