[pymvpa] RFE memory issue

Michael Hanke michael.hanke at gmail.com
Sat Nov 20 13:52:27 UTC 2010


On Sat, Nov 20, 2010 at 02:21:17PM +0100, Thorsten Kranz wrote:
> thank you for your quick and precise reply. I'll try your proposals on
> monday. But one question remains for me: what is the adequate way to
> group things together in chunks? All samples with the same label in
> one chunk? I must say that I didn't really make use of chunks up to
> now...

'chunks' are a way to group samples together that cannot be considered
independent of each other. For example, in fMRI data brain volume
acquired within a small time frame are heavily correlated for
"technical" reasons. 'chunks' can be used to group these together to
prevent samples from the same chunk to appear in training and testing
dataset at the same time, and therefore introducing an opportunistic
bias in the classification error.

How samples can be grouped into chunks in your dataset depends on the
properties of the data. If, for example, all samples are already
independent of any other you could create arbitrary groups of samples to
change the granularity of a cross-validation analysis -- e.g. always
having 10 samples in the test dataset instead of just one.



GPG key: 4096R/7FFB9E9B Michael Hanke

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