[pymvpa] Copying Mappingdata from multiple datasets

Nynke van der Laan nynkevanderlaan at gmail.com
Fri Jul 29 10:28:12 UTC 2011

Hello all,

I have a question regarding the construction of a new dataset from
samples/chunks/labels that were imported with NiftiDataset.
What I do for all (20 subjects) datasets, in a loop, is the following:
- import the functional dataset with NiftiDataset
- preprocess data (zscore, detrend, etc.)
- perform block averaging with SampleGroupMapper - > applyMapper

After that, I want to merge all these datasets into one dataset. For
this purpose I have vstacked all the samples (samples_temp), and
appended all the labels with eachother (labels_temp). I created a
chunk array with each subject being a chunk (to perform a leave one
subject out cross validation)
I have tried to combine the dataset_total with the following line of code:

dataset_total = Dataset(samples=samples_temp,
    labels = labels_temp, chunks = chunks_temp)

When I try to perform a searchlight analysis I get the following
message: "Searchlight only works with MappedDatasets that has metric

Thus, I suppose that the mapping from the functional scans (and it's
associated measures such as voxel size) are missing and the dataset I
created is not a MappedDataset. Although I did not manage to create a
MappedDataset, also not after consulting your information on

Do you have any suggestions?

Btw, I'm still using the older package on Neurodebian (this analysis
if for a revision and I prefer not to switch to a new version in
between revisions ;) )

Thanks in advance!

Nynke van der Laan

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