def generate(self, ds):
"""Yield dataset splits.
Parameters
----------
ds: Dataset
Input dataset
Returns
-------
generator
The generator yields every possible split according to the splitter
configuration. All generated dataset have a boolean 'lastsplit'
attribute in their dataset attribute collection indicating whether
this particular dataset is the last one.
"""
# localbinding
noslicing = self.__noslicing
count = self.__count
splattr = self.get_space()
ignore = self.__splitattr_ignore
# get attribute and source collection from dataset
splattr, collection = ds.get_attr(splattr)
splattr_data = splattr.value
cfgs = self.__splitattr_values
if cfgs is None:
cfgs = splattr.unique
if __debug__:
debug('SPL', 'Determined %i split specifications' % len(cfgs))
if not ignore is None:
# remove to be ignored bits
cfgs = [c for c in cfgs if not c in ignore]
if __debug__:
debug('SPL',
'%i split specifications left after removing ignored ones'
% len(cfgs))
n_cfgs = len(cfgs)
if self.__reverse:
if __debug__:
debug('SPL', 'Reversing split order')
cfgs = cfgs[::-1]
# split the data
for isplit, split in enumerate(cfgs):
if not count is None and isplit >= count:
# number of max splits is reached
if __debug__:
debug('SPL',
'Discard remaining splits as maximum of %i is reached'
% count)
break
# safeguard against 'split' being `None` -- in which case a single
# boolean would be the result of the comparision below, and not
# a boolean vector from element-wise comparision
if split is None:
split = [None]
# boolean mask is 'selected' samples for this split
filter_ = splattr_data == split
if not noslicing:
# check whether we can do slicing instead of advanced
# indexing -- if we can split the dataset without causing
# the data to be copied, its is quicker and leaner.
# However, it only works if we have a contiguous chunk or
# regular step sizes for the samples to be split
filter_ = mask2slice(filter_)
if collection is ds.sa:
if __debug__:
debug('SPL', 'Split along samples axis')
split_ds = ds[filter_]
elif collection is ds.fa:
if __debug__:
debug('SPL', 'Split along feature axis')
split_ds = ds[:, filter_]
else:
RuntimeError("This should never happen.")
# is this the last split
if count is None:
lastsplit = (isplit == n_cfgs - 1)
else:
lastsplit = (isplit == count - 1)
if not split_ds.a.has_key('lastsplit'):
# if not yet known -- add one
split_ds.a['lastsplit'] = lastsplit
else:
# otherwise just assign a new value
split_ds.a.lastsplit = lastsplit
yield split_ds
