# Changeset 10102:417b7322e9d3 in orange for Orange/statistics/estimate.py

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02/08/12 18:17:05 (2 years ago)
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Move Orange.statistics.estimate documentation to rst. Closes #1070.

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• ## Orange/statistics/estimate.py

 r10101 """ .. index:: Probability Estimation ======================================= Probability Estimation (estimate) ======================================= Probability estimators compute probabilities of values of class variable. They come in two flavours: #. for unconditional probabilities (:math:p(C=c), where :math:c is a class) and #. for conditional probabilities (:math:p(C=c|V=v), where :math:v is a feature value). A duality much like the one between learners and classifiers exists between probability estimator constructors and probability estimators: when a probability estimator constructor is called with data, it constructs a probability estimator that can then be called with a value of class variable to obtain a probability of that value. This duality is mainly needed to enable probability estimation for continuous variables, where it is not possible to generate a list of probabilities of all possible values in advance. First, probability estimation constructors for common probability estimation techniques are enumerated. Base classes, knowledge of which is needed to develop new techniques, are described later in this document. Probability Estimation Constructors =================================== .. class:: RelativeFrequency Bases: :class:EstimatorConstructor Compute distribution using relative frequencies of classes. :rtype: :class:EstimatorFromDistribution .. class:: Laplace Bases: :class:EstimatorConstructor Use Laplace estimation to compute distribution from frequencies of classes: .. math:: p(c) = \\frac{Nc+1}{N+n} where :math:Nc is number of occurrences of an event (e.g. number of instances in class c), :math:N is the total number of events (instances) and :math:n is the number of different events (classes). :rtype: :class:EstimatorFromDistribution .. class:: M Bases: :class:EstimatorConstructor .. method:: __init__(m) :param m: Parameter for m-estimation. :type m: int Use m-estimation to compute distribution from frequencies of classes: .. math:: p(c) = \\frac{Nc+m*ap(c)}{N+m} where :math:Nc is number of occurrences of an event (e.g. number of instances in class c), :math:N is the total number of events (instances) and :math:ap(c) is the prior probability of event (class) c. :rtype: :class:EstimatorFromDistribution .. class:: Kernel Bases: :class:EstimatorConstructor .. method:: __init__(min_impact, smoothing, n_points) :param min_impact: A requested minimal weight of a point (default: 0.01); points with lower weights won't be taken into account. :type min_impact: float :param smoothing: Smoothing factor (default: 1.144). :type smoothing: float :param n_points: Number of points for the interpolating curve. If negative, say -3 (default), 3 points will be inserted between each data points. :type n_points: int Compute probabilities for continuous variable for certain number of points using Gaussian kernels. The resulting point-wise continuous distribution is stored as :class:~Orange.statistics.distribution.Continuous. Probabilities are always computed at all points that are present in the data (i.e. the existing values of the continuous feature). If :obj:n_points is positive and greater than the number of existing data points, additional points are inserted between the existing points to achieve the required number of points. Approximately equal number of new points is inserted between each adjacent existing point each data points. If :obj:n_points is negative, its absolute value determines the number of points to be added between each two data points. :rtype: :class:EstimatorFromDistribution .. class:: Loess Bases: :class:EstimatorConstructor .. method:: __init__(window_proportion, n_points) :param window_proportion: A proportion of points in a window. :type window_proportion: float :param n_points: Number of points for the interpolating curve. If negative, say -3 (default), 3 points will be inserted between each data points. :type n_points: int Prepare a probability estimator that computes probability at point x as weighted local regression of probabilities for points in the window around this point. The window contains a prescribed proportion of original data points. The window is as symmetric as possible in the sense that the leftmost point in the window is approximately as far from x as the rightmost. The number of points to the left of x might thus differ from the number of points to the right. Points are weighted by bi-cubic weight function; a weight of point at x' is :math:(1-|t|^3)^3, where :math:t is :math:(x-x'>)/h and :math:h is the distance to the farther of the two window edge points. :rtype: :class:EstimatorFromDistribution .. class:: ConditionalLoess Bases: :class:ConditionalEstimatorConstructor .. method:: __init__(window_proportion, n_points) :param window_proportion: A proportion of points in a window. :type window_proportion: float :param n_points: Number of points for the interpolating curve. If negative, say -3 (default), 3 points will be inserted between each data points. :type n_points: int Construct a conditional probability estimator, in other aspects similar to the one constructed by :class:Loess. :rtype: :class:ConditionalEstimatorFromDistribution. Base classes ============= All probability estimators are derived from two base classes: one for unconditional and the other for conditional probability estimation. The same is true for probability estimator constructors. .. class:: EstimatorConstructor Constructor of an unconditional probability estimator. .. method:: __call__([distribution[, apriori]], [instances[, weight_id]]) :param distribution: input distribution. :type distribution: :class:~Orange.statistics.distribution.Distribution :param apriori: prior distribution. :type distribution: :class:~Orange.statistics.distribution.Distribution :param instances: input data. :type distribution: :class:Orange.data.Table :param weight_id: ID of the weight attribute. :type weight_id: int If distribution is given, it can be followed by prior class distribution. Similarly, instances can be followed by with the ID of meta attribute with instance weights. (Hint: to pass a prior distribution and instances, but no distribution, just pass :obj:None for the latter.) When both, distribution and instances are given, it is up to constructor to decide what to use. .. class:: Estimator .. attribute:: supports_discrete Tells whether the estimator can handle discrete attributes. .. attribute:: supports_continuous Tells whether the estimator can handle continuous attributes. .. method:: __call__([value]) If value is given, return the probability of the value. :rtype: float If the value is omitted, an attempt is made to return a distribution of probabilities for all values. :rtype: :class:~Orange.statistics.distribution.Distribution (usually :class:~Orange.statistics.distribution.Discrete for discrete and :class:~Orange.statistics.distribution.Continuous for continuous) or :obj:NoneType .. class:: ConditionalEstimatorConstructor Constructor of a conditional probability estimator. .. method:: __call__([table[, apriori]], [instances[, weight_id]]) :param table: input distribution. :type table: :class:Orange.statistics.contingency.Table :param apriori: prior distribution. :type distribution: :class:~Orange.statistics.distribution.Distribution :param instances: input data. :type distribution: :class:Orange.data.Table :param weight_id: ID of the weight attribute. :type weight_id: int If distribution is given, it can be followed by prior class distribution. Similarly, instances can be followed by with the ID of meta attribute with instance weights. (Hint: to pass a prior distribution and instances, but no distribution, just pass :obj:None for the latter.) When both, distribution and instances are given, it is up to constructor to decide what to use. .. class:: ConditionalEstimator As a counterpart of :class:Estimator, this estimator can return conditional probabilities. .. method:: __call__([[value,] condition_value]) When given two values, it returns a probability of :math:p(value|condition). :rtype: float When given only one value, it is interpreted as condition; the estimator attempts to return a distribution of conditional probabilities for all values. :rtype: :class:~Orange.statistics.distribution.Distribution (usually :class:~Orange.statistics.distribution.Discrete for discrete and :class:~Orange.statistics.distribution.Continuous for continuous) or :obj:NoneType When called without arguments, it returns a matrix containing probabilities :math:p(value|condition) for each possible :math:value and :math:condition (a contingency table); condition is used as outer variable. :rtype: :class:Orange.statistics.contingency.Table or :obj:NoneType If estimator cannot return precomputed distributions and/or contingencies, it returns :obj:None. Common Components ================= .. class:: EstimatorFromDistribution Bases: :class:Estimator Probability estimator constructors that compute probabilities for all values in advance return this estimator with calculated quantities in the :obj:probabilities attribute. .. attribute:: probabilities A precomputed list of probabilities. .. method:: __call__([value]) If value is given, return the probability of the value. For discrete variables, every value has an entry in the :obj:probabilities attribute. For continuous variables, a linear interpolation between two nearest points is used to compute the probability. :rtype: float If the value is omitted, a copy of :obj:probabilities is returned. :rtype: :class:~Orange.statistics.distribution.Distribution (usually :class:~Orange.statistics.distribution.Discrete for discrete and :class:~Orange.statistics.distribution.Continuous for continuous). .. class:: ConditionalEstimatorFromDistribution Bases: :class:ConditionalEstimator Probability estimator constructors that compute the whole contingency table (:class:Orange.statistics.contingency.Table) of conditional probabilities in advance return this estimator with the table in the :obj:probabilities attribute. .. attribute:: probabilities A precomputed contingency table. .. method:: __call__([[value,] condition_value]) For detailed description of handling of different combinations of parameters, see the inherited :obj:ConditionalEstimator.__call__. For behaviour with continuous variable distributions, see the unconditional counterpart :obj:EstimatorFromDistribution.__call__. .. class:: ConditionalByRows Bases: :class:ConditionalEstimator .. attribute:: estimator_constructor An unconditional probability estimator constructor. Computes a conditional probability estimator using an unconditional probability estimator constructor. The result can be of type :class:ConditionalEstimatorFromDistribution or :class:ConditionalEstimatorByRows, depending on the type of constructor. .. method:: __call__([table[, apriori]], [instances[, weight_id]], estimator) :param table: input distribution. :type table: :class:Orange.statistics.contingency.Table :param apriori: prior distribution. :type distribution: :class:~Orange.statistics.distribution.Distribution :param instances: input data. :type distribution: :class:Orange.data.Table :param weight_id: ID of the weight attribute. :type weight_id: int :param estimator: unconditional probability estimator constructor. :type estimator: :class:EstimatorConstructor Compute contingency matrix if it has not been computed already. Then call :obj:estimator_constructor for each value of condition attribute. If all constructed estimators can return distribution of probabilities for all classes (usually either all or none can), the :class:~Orange.statistics.distribution.Distribution instances are put in a contingency table and :class:ConditionalEstimatorFromDistribution is constructed and returned. If constructed estimators are not capable of returning distribution of probabilities, a :class:ConditionalEstimatorByRows is constructed and the estimators are stored in its :obj:estimator_list. :rtype: :class:ConditionalEstimatorFromDistribution or :class:ConditionalEstimatorByRows .. class:: ConditionalEstimatorByRows Bases: :class:ConditionalEstimator A conditional probability estimator constructors that itself uses a series of estimators, one for each possible condition, stored in its :obj:estimator_list attribute. .. attribute:: estimator_list A list of estimators; one for each value of :obj:condition. .. method:: __call__([[value,] condition_value]) Uses estimators from :obj:estimator_list, depending on given condition_value. For detailed description of handling of different combinations of parameters, see the inherited :obj:ConditionalEstimator.__call__. """ import Orange from Orange.core import ProbabilityEstimator as Estimator
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