| Multivariate Pattern Analysis in Python

### Navigation

- index
- next |
- previous |
- ExpPsy Project |
- NeuroDebian Project |
- PyMVPA 0.4.x Home |
- PyMVPA Home |
- Documentation »
- Module Reference »

This content refers to the previous stable release of PyMVPA. Please visit www.pymvpa.org for the most recent version of PyMVPA and its documentation.

# featsel.helpers

## Module: `featsel.helpers`

Inheritance diagram for `mvpa.featsel.helpers`:

## Classes

### `BestDetector`

class `mvpa.featsel.helpers.``BestDetector`(func=<built-in function min>, lastminimum=False)

  Bases: `object`

  Determine whether the last value in a sequence is the best one given some criterion.

  Initialize with number of steps

  Parameters:

  - fun (functor) – Functor to select the best results. Defaults to min
  - lastminimum (bool) – Toggle whether the latest or the earliest minimum is used as optimal value to determine the stopping criterion.

  `bestindex`

### `ElementSelector`

class `mvpa.featsel.helpers.``ElementSelector`(mode='discard', **kwargs)

  Bases: `mvpa.misc.state.ClassWithCollections`

  Base class to implement functors to select some elements based on a sequence of values.

  Note

  Available state variables:

  - True+: Store number of discarded elements.

  (States enabled by default are listed with +)

  See also

  Please refer to the documentation of the base class for more information:

  `ClassWithCollections`

  Cheap initialization.

  Parameters:

  - mode ([‘discard’, ‘select’]) – Decides whether to select or to discard features.
  - enable_states (None or list of basestring) – Names of the state variables which should be enabled additionally to default ones
  - disable_states (None or list of basestring) – Names of the state variables which should be disabled

  `mode`

### `FixedErrorThresholdStopCrit`

class `mvpa.featsel.helpers.``FixedErrorThresholdStopCrit`(threshold)

  Bases: `mvpa.featsel.helpers.StoppingCriterion`

  Stop computation if the latest error drops below a certain threshold.

  Initialize with threshold.

  Parameters: | threshold (float [0,1]) – Error threshold.

  `threshold`

### `FixedNElementTailSelector`

class `mvpa.featsel.helpers.``FixedNElementTailSelector`(nelements, **kwargs)

  Bases: `mvpa.featsel.helpers.TailSelector`

  Given a sequence, provide set of IDs for a fixed number of to be selected elements.

  Note

  Available state variables:

  - True+: Store number of discarded elements.

  (States enabled by default are listed with +)

  See also

  Please refer to the documentation of the base class for more information:

  `TailSelector`

  Cheap initialization.

  Parameters:

  - nelements (int) – Number of elements to select/discard.
  - enable_states (None or list of basestring) – Names of the state variables which should be enabled additionally to default ones
  - disable_states (None or list of basestring) – Names of the state variables which should be disabled
  - tail ([‘lower’, ‘upper’]) – Choose the tail to be processed.
  - sort (bool) – Flag whether selected IDs will be sorted. Disable if not necessary to save some CPU cycles.
  - mode ([‘discard’, ‘select’]) – Decides whether to select or to discard features.

  `nelements`

### `FractionTailSelector`

class `mvpa.featsel.helpers.``FractionTailSelector`(felements, **kwargs)

  Bases: `mvpa.featsel.helpers.TailSelector`

  Given a sequence, provide Ids for a fraction of elements

  Note

  Available state variables:

  - True+: Store number of discarded elements.

  (States enabled by default are listed with +)

  See also

  Please refer to the documentation of the base class for more information:

  `TailSelector`

  Cheap initialization.

  Parameters:

  - felements (float (0,1.0]) – Fraction of elements to select/discard. Note: Even when 0.0 is specified at least one element will be selected.
  - enable_states (None or list of basestring) – Names of the state variables which should be enabled additionally to default ones
  - disable_states (None or list of basestring) – Names of the state variables which should be disabled
  - tail ([‘lower’, ‘upper’]) – Choose the tail to be processed.
  - sort (bool) – Flag whether selected IDs will be sorted. Disable if not necessary to save some CPU cycles.
  - mode ([‘discard’, ‘select’]) – Decides whether to select or to discard features.

  `felements`

### `MultiStopCrit`

class `mvpa.featsel.helpers.``MultiStopCrit`(crits, mode='or')

  Bases: `mvpa.featsel.helpers.StoppingCriterion`

  Stop computation if the latest error drops below a certain threshold.

  Parameters:

  - crits (list of StoppingCriterion instances) – For each call to MultiStopCrit all of these criterions will be evaluated.
  - mode (any of (‘and’, ‘or’)) – Logical function to determine the multi criterion from the set of base criteria.

### `NBackHistoryStopCrit`

class `mvpa.featsel.helpers.``NBackHistoryStopCrit`(bestdetector=<mvpa.featsel.helpers.BestDetector object at 0xbfac16c>, steps=10)

  Bases: `mvpa.featsel.helpers.StoppingCriterion`

  Stop computation if for a number of steps error was increasing

  Initialize with number of steps

  Parameters:

  - bestdetector (BestDetector instance) – used to determine where the best error is located.
  - steps (int) – How many steps to check after optimal value.

  `steps`

### `NStepsStopCrit`

class `mvpa.featsel.helpers.``NStepsStopCrit`(steps)

  Bases: `mvpa.featsel.helpers.StoppingCriterion`

  Stop computation after a certain number of steps.

  Initialize with number of steps.

  Parameters: | steps (int) – Number of steps after which to stop.

  `steps`

### `RangeElementSelector`

class `mvpa.featsel.helpers.``RangeElementSelector`(lower=None, upper=None, inclusive=False, mode='select', **kwargs)

  Bases: `mvpa.featsel.helpers.ElementSelector`

  Select elements based on specified range of values

  Note

  Available state variables:

  - True+: Store number of discarded elements.

  (States enabled by default are listed with +)

  See also

  Please refer to the documentation of the base class for more information:

  `ElementSelector`

  Initialization RangeElementSelector

  Parameters:

  - lower – If not None – select elements which are above of specified value
  - upper – If not None – select elements which are lower of specified value
  - inclusive – Either to include end points
  - mode – overrides parent’s default to be ‘select’ since it is more native for RangeElementSelector XXX TODO – unify??
  - enable_states (None or list of basestring) – Names of the state variables which should be enabled additionally to default ones
  - disable_states (None or list of basestring) – Names of the state variables which should be disabled

  upper could be lower than lower – then selection is done on values <= lower or >=upper (ie tails). This would produce the same result if called with flipped values for mode and inclusive.

  If no upper no lower is set, assuming upper,lower=0, thus outputing non-0 elements

### `StoppingCriterion`

class `mvpa.featsel.helpers.``StoppingCriterion`

  Bases: `object`

  Base class for all functors to decide when to stop RFE (or may be general optimization... so it probably will be moved out into some other module

### `TailSelector`

class `mvpa.featsel.helpers.``TailSelector`(tail='lower', sort=True, **kwargs)

  Bases: `mvpa.featsel.helpers.ElementSelector`

  Select elements from a tail of a distribution.

  The default behaviour is to discard the lower tail of a given distribution.

  Note

  Available state variables:

  - True+: Store number of discarded elements.

  (States enabled by default are listed with +)

  See also

  Please refer to the documentation of the base class for more information:

  `ElementSelector`

  Initialize TailSelector

  Parameters:

  - tail ([‘lower’, ‘upper’]) – Choose the tail to be processed.
  - sort (bool) – Flag whether selected IDs will be sorted. Disable if not necessary to save some CPU cycles.
  - enable_states (None or list of basestring) – Names of the state variables which should be enabled additionally to default ones
  - disable_states (None or list of basestring) – Names of the state variables which should be disabled
  - mode ([‘discard’, ‘select’]) – Decides whether to select or to discard features.

### Navigation

- index
- next |
- previous |
- ExpPsy Project |
- NeuroDebian Project |
- PyMVPA 0.4.x Home |
- PyMVPA Home |
- Documentation »
- Module Reference »