def __init__(self,
fmeasure,
pmeasure,
splitter,
fselector,
stopping_criterion=NBackHistoryStopCrit(BestDetector()),
bestdetector=BestDetector(),
train_pmeasure=True,
# XXX should we may be guard splitter so we do not end up
# with inappropriate one for the use, i.e. which
# generates more than 2 splits
# guard_splitter=True,
**kwargs
):
"""
Parameters
----------
fmeasure : Measure
Computed for each candidate feature selection. The measure has
to compute a scalar value.
pmeasure : Measure
Compute against a test dataset for each incremental feature
set.
splitter: Splitter
This splitter instance has to generate at least one dataset split
when called with the input dataset that is used to compute the
per-feature criterion for feature selection.
bestdetector : Functor
Given a list of error values it has to return a boolean that
signals whether the latest error value is the total minimum.
stopping_criterion : Functor
Given a list of error values it has to return whether the
criterion is fulfilled.
fselector : Functor
train_clf : bool
Flag whether the classifier in `transfer_error` should be
trained before computing the error. In general this is
required, but if the `sensitivity_analyzer` and
`transfer_error` share and make use of the same classifier it
can be switched off to save CPU cycles. Default `None` checks
if sensitivity_analyzer is based on a classifier and doesn't train
if so.
"""
# bases init first
FeatureSelection.__init__(self, **kwargs)
self._fmeasure = fmeasure
self._pmeasure = pmeasure
self._splitter = splitter
self._fselector = fselector
self._stopping_criterion = stopping_criterion
self._bestdetector = bestdetector
self._train_pmeasure = train_pmeasure
def test_n_back_history_stop_crit(self):
"""Test stopping criterion"""
stopcrit = NBackHistoryStopCrit()
# for empty history -- no best but just go
self.assertTrue(stopcrit([]) == False)
# should not stop if we got 10 more after minimal
self.assertTrue(
stopcrit([1, 0.9, 0.8] + [0.9] * (stopcrit.steps - 1)) == False)
# should stop if we got 10 more after minimal
self.assertTrue(
stopcrit([1, 0.9, 0.8] + [0.9] * stopcrit.steps) == True)
# test for alternative func
stopcrit = NBackHistoryStopCrit(BestDetector(func=max))
self.assertTrue(stopcrit([0.8, 0.9, 1.0] + [0.9] * 9) == False)
self.assertTrue(stopcrit([0.8, 0.9, 1.0] + [0.9] * 10) == True)
# test to detect earliest and latest minimum
stopcrit = NBackHistoryStopCrit(BestDetector(lastminimum=True))
self.assertTrue(stopcrit([3, 2, 1, 1, 1, 2, 1]) == False)
stopcrit = NBackHistoryStopCrit(steps=4)
self.assertTrue(stopcrit([3, 2, 1, 1, 1, 2, 1]) == True)
def test_multi_stop_crit(self):
"""Test multiple stop criteria"""
stopcrit = MultiStopCrit(
[FixedErrorThresholdStopCrit(0.5),
NBackHistoryStopCrit(steps=4)])
# default 'or' mode
# nback triggers
self.assertTrue(stopcrit([1, 0.9, 0.8] + [0.9] * 4) == True)
# threshold triggers
self.assertTrue(stopcrit([1, 0.9, 0.2]) == True)
# alternative 'and' mode
stopcrit = MultiStopCrit(
[FixedErrorThresholdStopCrit(0.5),
NBackHistoryStopCrit(steps=4)],
mode='and')
# nback triggers not
self.assertTrue(stopcrit([1, 0.9, 0.8] + [0.9] * 4) == False)
# threshold triggers not
self.assertTrue(stopcrit([1, 0.9, 0.2]) == False)
# only both satisfy
self.assertTrue(stopcrit([1, 0.9, 0.4] + [0.4] * 4) == True)
def test_rfe_sensmap():
# http://lists.alioth.debian.org/pipermail/pkg-exppsy-pymvpa/2013q3/002538.html
# just a smoke test. fails with
from mvpa2.clfs.svm import LinearCSVMC
from mvpa2.clfs.meta import FeatureSelectionClassifier
from mvpa2.measures.base import CrossValidation, RepeatedMeasure
from mvpa2.generators.splitters import Splitter
from mvpa2.generators.partition import NFoldPartitioner
from mvpa2.misc.errorfx import mean_mismatch_error
from mvpa2.mappers.fx import mean_sample
from mvpa2.mappers.fx import maxofabs_sample
from mvpa2.generators.base import Repeater
from mvpa2.featsel.rfe import RFE
from mvpa2.featsel.helpers import FractionTailSelector, BestDetector
from mvpa2.featsel.helpers import NBackHistoryStopCrit
from mvpa2.datasets import vstack
from mvpa2.misc.data_generators import normal_feature_dataset
# Let's simulate the beast -- 6 categories total groupped into 3
# super-ordinate, and actually without any 'superordinate' effect
# since subordinate categories independent
fds = normal_feature_dataset(nlabels=3,
snr=1, # 100, # pure signal! ;)
perlabel=9,
nfeatures=6,
nonbogus_features=range(3),
nchunks=3)
clfsvm = LinearCSVMC()
rfesvm = RFE(clfsvm.get_sensitivity_analyzer(postproc=maxofabs_sample()),
CrossValidation(
clfsvm,
NFoldPartitioner(),
errorfx=mean_mismatch_error, postproc=mean_sample()),
Repeater(2),
fselector=FractionTailSelector(0.70, mode='select', tail='upper'),
stopping_criterion=NBackHistoryStopCrit(BestDetector(), 10),
update_sensitivity=True)
fclfsvm = FeatureSelectionClassifier(clfsvm, rfesvm)
sensanasvm = fclfsvm.get_sensitivity_analyzer(postproc=maxofabs_sample())
# manually repeating/splitting so we do both RFE sensitivity and classification
senses, errors = [], []
for i, pset in enumerate(NFoldPartitioner().generate(fds)):
# split partitioned dataset
split = [d for d in Splitter('partitions').generate(pset)]
senses.append(sensanasvm(split[0])) # and it also should train the classifier so we would ask it about error
errors.append(mean_mismatch_error(fclfsvm.predict(split[1]), split[1].targets))
senses = vstack(senses)
errors = vstack(errors)
# Let's compare against rerunning the beast simply for classification with CV
errors_cv = CrossValidation(fclfsvm, NFoldPartitioner(), errorfx=mean_mismatch_error)(fds)
# and they should match
assert_array_equal(errors, errors_cv)
# buggy!
cv_sensana_svm = RepeatedMeasure(sensanasvm, NFoldPartitioner())
senses_rm = cv_sensana_svm(fds)
#print senses.samples, senses_rm.samples
#print errors, errors_cv.samples
assert_raises(AssertionError,
assert_array_almost_equal,
senses.samples, senses_rm.samples)
raise SkipTest("Known failure for repeated measures: https://github.com/PyMVPA/PyMVPA/issues/117")
def test_rfe(self, clf):
# sensitivity analyser and transfer error quantifier use the SAME clf!
sens_ana = clf.get_sensitivity_analyzer(postproc=maxofabs_sample())
pmeasure = ProxyMeasure(clf,
postproc=BinaryFxNode(mean_mismatch_error,
'targets'))
cvmeasure = CrossValidation(clf,
NFoldPartitioner(),
errorfx=mean_mismatch_error,
postproc=mean_sample())
rfesvm_split = SplitClassifier(clf, OddEvenPartitioner())
# explore few recipes
for rfe, data in [
# because the clf is already trained when computing the sensitivity
# map, prevent retraining for transfer error calculation
# Use absolute of the svm weights as sensitivity
(RFE(sens_ana,
pmeasure,
Splitter('train'),
fselector=FixedNElementTailSelector(1),
train_pmeasure=False), self.get_data()),
# use cross-validation within training to get error for the stopping point
# but use full training data to derive sensitivity
(
RFE(
sens_ana,
cvmeasure,
Repeater(
2
), # give the same full dataset to sens_ana and cvmeasure
fselector=FractionTailSelector(0.70,
mode='select',
tail='upper'),
train_pmeasure=True),
normal_feature_dataset(perlabel=20,
nchunks=5,
nfeatures=200,
nonbogus_features=[0, 1],
snr=1.5)),
# use cross-validation (via SplitClassifier) and get mean
# of normed sensitivities across those splits
(
RFE(
rfesvm_split.get_sensitivity_analyzer(
postproc=ChainMapper([
FxMapper('features', l2_normed),
FxMapper('samples', np.mean),
FxMapper('samples', np.abs)
])),
ConfusionBasedError(rfesvm_split, confusion_state='stats'),
Repeater(
2), # we will use the same full cv-training dataset
fselector=FractionTailSelector(0.50,
mode='select',
tail='upper'),
stopping_criterion=NBackHistoryStopCrit(
BestDetector(), 10),
train_pmeasure=
False, # we just extract it from existing confusion
update_sensitivity=True),
normal_feature_dataset(perlabel=28,
nchunks=7,
nfeatures=200,
nonbogus_features=[0, 1],
snr=1.5))
]:
# prep data
# data = datasets['uni2medium']
data_nfeatures = data.nfeatures
rfe.train(data)
resds = rfe(data)
# fail if orig datasets are changed
self.assertTrue(data.nfeatures == data_nfeatures)
# check that the features set with the least error is selected
if len(rfe.ca.errors):
e = np.array(rfe.ca.errors)
if isinstance(rfe._fselector, FixedNElementTailSelector):
self.assertTrue(resds.nfeatures == data_nfeatures -
e.argmin())
else:
imin = np.argmin(e)
if 'does_feature_selection' in clf.__tags__:
# if clf is smart it might figure it out right away
assert_array_less(imin, len(e))
else:
# in this case we can even check if we had actual
# going down/up trend... although -- why up???
self.assertTrue(1 < imin < len(e) - 1)
else:
self.assertTrue(resds.nfeatures == data_nfeatures)
# silly check if nfeatures is in decreasing order
nfeatures = np.array(rfe.ca.nfeatures).copy()
nfeatures.sort()
self.assertTrue((nfeatures[::-1] == rfe.ca.nfeatures).all())
# check if history has elements for every step
self.assertTrue(
set(rfe.ca.history) == set(range(len(np.array(
rfe.ca.errors)))))
# Last (the largest number) can be present multiple times even
# if we remove 1 feature at a time -- just need to stop well
# in advance when we have more than 1 feature left ;)
self.assertTrue(rfe.ca.nfeatures[-1] == len(
np.where(rfe.ca.history == max(rfe.ca.history))[0]))