# coding: utf-8 # Author: Johannes Schönberger # # License: BSD 3 clause import numpy as np import warnings from ..base import BaseEstimator, MetaEstimatorMixin, RegressorMixin, clone from ..base import MultiOutputMixin from ..utils import check_random_state, check_consistent_length from ..utils.random import sample_without_replacement from ..utils.validation import check_is_fitted, _check_sample_weight from ..utils.validation import _deprecate_positional_args from ._base import LinearRegression from ..utils.validation import has_fit_parameter from ..exceptions import ConvergenceWarning _EPSILON = np.spacing(1) def _dynamic_max_trials(n_inliers, n_samples, min_samples, probability): """Determine number trials such that at least one outlier-free subset is sampled for the given inlier/outlier ratio. Parameters ---------- n_inliers : int Number of inliers in the data. n_samples : int Total number of samples in the data. min_samples : int Minimum number of samples chosen randomly from original data. probability : float Probability (confidence) that one outlier-free sample is generated. Returns ------- trials : int Number of trials. """ inlier_ratio = n_inliers / float(n_samples) nom = max(_EPSILON, 1 - probability) denom = max(_EPSILON, 1 - inlier_ratio ** min_samples) if nom == 1: return 0 if denom == 1: return float('inf') return abs(float(np.ceil(np.log(nom) / np.log(denom)))) class RANSACRegressor(MetaEstimatorMixin, RegressorMixin, MultiOutputMixin, BaseEstimator): """RANSAC (RANdom SAmple Consensus) algorithm. RANSAC is an iterative algorithm for the robust estimation of parameters from a subset of inliers from the complete data set. Read more in the :ref:`User Guide `. Parameters ---------- base_estimator : object, default=None Base estimator object which implements the following methods: * `fit(X, y)`: Fit model to given training data and target values. * `score(X, y)`: Returns the mean accuracy on the given test data, which is used for the stop criterion defined by `stop_score`. Additionally, the score is used to decide which of two equally large consensus sets is chosen as the better one. * `predict(X)`: Returns predicted values using the linear model, which is used to compute residual error using loss function. If `base_estimator` is None, then :class:`~sklearn.linear_model.LinearRegression` is used for target values of dtype float. Note that the current implementation only supports regression estimators. min_samples : int (>= 1) or float ([0, 1]), default=None Minimum number of samples chosen randomly from original data. Treated as an absolute number of samples for `min_samples >= 1`, treated as a relative number `ceil(min_samples * X.shape[0]`) for `min_samples < 1`. This is typically chosen as the minimal number of samples necessary to estimate the given `base_estimator`. By default a ``sklearn.linear_model.LinearRegression()`` estimator is assumed and `min_samples` is chosen as ``X.shape[1] + 1``. residual_threshold : float, default=None Maximum residual for a data sample to be classified as an inlier. By default the threshold is chosen as the MAD (median absolute deviation) of the target values `y`. is_data_valid : callable, default=None This function is called with the randomly selected data before the model is fitted to it: `is_data_valid(X, y)`. If its return value is False the current randomly chosen sub-sample is skipped. is_model_valid : callable, default=None This function is called with the estimated model and the randomly selected data: `is_model_valid(model, X, y)`. If its return value is False the current randomly chosen sub-sample is skipped. Rejecting samples with this function is computationally costlier than with `is_data_valid`. `is_model_valid` should therefore only be used if the estimated model is needed for making the rejection decision. max_trials : int, default=100 Maximum number of iterations for random sample selection. max_skips : int, default=np.inf Maximum number of iterations that can be skipped due to finding zero inliers or invalid data defined by ``is_data_valid`` or invalid models defined by ``is_model_valid``. .. versionadded:: 0.19 stop_n_inliers : int, default=np.inf Stop iteration if at least this number of inliers are found. stop_score : float, default=np.inf Stop iteration if score is greater equal than this threshold. stop_probability : float in range [0, 1], default=0.99 RANSAC iteration stops if at least one outlier-free set of the training data is sampled in RANSAC. This requires to generate at least N samples (iterations):: N >= log(1 - probability) / log(1 - e**m) where the probability (confidence) is typically set to high value such as 0.99 (the default) and e is the current fraction of inliers w.r.t. the total number of samples. loss : string, callable, default='absolute_loss' String inputs, "absolute_loss" and "squared_loss" are supported which find the absolute loss and squared loss per sample respectively. If ``loss`` is a callable, then it should be a function that takes two arrays as inputs, the true and predicted value and returns a 1-D array with the i-th value of the array corresponding to the loss on ``X[i]``. If the loss on a sample is greater than the ``residual_threshold``, then this sample is classified as an outlier. .. versionadded:: 0.18 random_state : int, RandomState instance, default=None The generator used to initialize the centers. Pass an int for reproducible output across multiple function calls. See :term:`Glossary `. Attributes ---------- estimator_ : object Best fitted model (copy of the `base_estimator` object). n_trials_ : int Number of random selection trials until one of the stop criteria is met. It is always ``<= max_trials``. inlier_mask_ : bool array of shape [n_samples] Boolean mask of inliers classified as ``True``. n_skips_no_inliers_ : int Number of iterations skipped due to finding zero inliers. .. versionadded:: 0.19 n_skips_invalid_data_ : int Number of iterations skipped due to invalid data defined by ``is_data_valid``. .. versionadded:: 0.19 n_skips_invalid_model_ : int Number of iterations skipped due to an invalid model defined by ``is_model_valid``. .. versionadded:: 0.19 Examples -------- >>> from sklearn.linear_model import RANSACRegressor >>> from sklearn.datasets import make_regression >>> X, y = make_regression( ... n_samples=200, n_features=2, noise=4.0, random_state=0) >>> reg = RANSACRegressor(random_state=0).fit(X, y) >>> reg.score(X, y) 0.9885... >>> reg.predict(X[:1,]) array([-31.9417...]) References ---------- .. [1] https://en.wikipedia.org/wiki/RANSAC .. [2] https://www.sri.com/sites/default/files/publications/ransac-publication.pdf .. [3] http://www.bmva.org/bmvc/2009/Papers/Paper355/Paper355.pdf """ @_deprecate_positional_args def __init__(self, base_estimator=None, *, min_samples=None, residual_threshold=None, is_data_valid=None, is_model_valid=None, max_trials=100, max_skips=np.inf, stop_n_inliers=np.inf, stop_score=np.inf, stop_probability=0.99, loss='absolute_loss', random_state=None): self.base_estimator = base_estimator self.min_samples = min_samples self.residual_threshold = residual_threshold self.is_data_valid = is_data_valid self.is_model_valid = is_model_valid self.max_trials = max_trials self.max_skips = max_skips self.stop_n_inliers = stop_n_inliers self.stop_score = stop_score self.stop_probability = stop_probability self.random_state = random_state self.loss = loss def fit(self, X, y, sample_weight=None): """Fit estimator using RANSAC algorithm. Parameters ---------- X : array-like or sparse matrix, shape [n_samples, n_features] Training data. y : array-like of shape (n_samples,) or (n_samples, n_targets) Target values. sample_weight : array-like of shape (n_samples,), default=None Individual weights for each sample raises error if sample_weight is passed and base_estimator fit method does not support it. .. versionadded:: 0.18 Raises ------ ValueError If no valid consensus set could be found. This occurs if `is_data_valid` and `is_model_valid` return False for all `max_trials` randomly chosen sub-samples. """ # Need to validate separately here. # We can't pass multi_ouput=True because that would allow y to be csr. check_X_params = dict(accept_sparse='csr') check_y_params = dict(ensure_2d=False) X, y = self._validate_data(X, y, validate_separately=(check_X_params, check_y_params)) check_consistent_length(X, y) if self.base_estimator is not None: base_estimator = clone(self.base_estimator) else: base_estimator = LinearRegression() if self.min_samples is None: # assume linear model by default min_samples = X.shape[1] + 1 elif 0 < self.min_samples < 1: min_samples = np.ceil(self.min_samples * X.shape[0]) elif self.min_samples >= 1: if self.min_samples % 1 != 0: raise ValueError("Absolute number of samples must be an " "integer value.") min_samples = self.min_samples else: raise ValueError("Value for `min_samples` must be scalar and " "positive.") if min_samples > X.shape[0]: raise ValueError("`min_samples` may not be larger than number " "of samples: n_samples = %d." % (X.shape[0])) if self.stop_probability < 0 or self.stop_probability > 1: raise ValueError("`stop_probability` must be in range [0, 1].") if self.residual_threshold is None: # MAD (median absolute deviation) residual_threshold = np.median(np.abs(y - np.median(y))) else: residual_threshold = self.residual_threshold if self.loss == "absolute_loss": if y.ndim == 1: loss_function = lambda y_true, y_pred: np.abs(y_true - y_pred) else: loss_function = lambda \ y_true, y_pred: np.sum(np.abs(y_true - y_pred), axis=1) elif self.loss == "squared_loss": if y.ndim == 1: loss_function = lambda y_true, y_pred: (y_true - y_pred) ** 2 else: loss_function = lambda \ y_true, y_pred: np.sum((y_true - y_pred) ** 2, axis=1) elif callable(self.loss): loss_function = self.loss else: raise ValueError( "loss should be 'absolute_loss', 'squared_loss' or a callable." "Got %s. " % self.loss) random_state = check_random_state(self.random_state) try: # Not all estimator accept a random_state base_estimator.set_params(random_state=random_state) except ValueError: pass estimator_fit_has_sample_weight = has_fit_parameter(base_estimator, "sample_weight") estimator_name = type(base_estimator).__name__ if (sample_weight is not None and not estimator_fit_has_sample_weight): raise ValueError("%s does not support sample_weight. Samples" " weights are only used for the calibration" " itself." % estimator_name) if sample_weight is not None: sample_weight = _check_sample_weight(sample_weight, X) n_inliers_best = 1 score_best = -np.inf inlier_mask_best = None X_inlier_best = None y_inlier_best = None inlier_best_idxs_subset = None self.n_skips_no_inliers_ = 0 self.n_skips_invalid_data_ = 0 self.n_skips_invalid_model_ = 0 # number of data samples n_samples = X.shape[0] sample_idxs = np.arange(n_samples) self.n_trials_ = 0 max_trials = self.max_trials while self.n_trials_ < max_trials: self.n_trials_ += 1 if (self.n_skips_no_inliers_ + self.n_skips_invalid_data_ + self.n_skips_invalid_model_) > self.max_skips: break # choose random sample set subset_idxs = sample_without_replacement(n_samples, min_samples, random_state=random_state) X_subset = X[subset_idxs] y_subset = y[subset_idxs] # check if random sample set is valid if (self.is_data_valid is not None and not self.is_data_valid(X_subset, y_subset)): self.n_skips_invalid_data_ += 1 continue # fit model for current random sample set if sample_weight is None: base_estimator.fit(X_subset, y_subset) else: base_estimator.fit(X_subset, y_subset, sample_weight=sample_weight[subset_idxs]) # check if estimated model is valid if (self.is_model_valid is not None and not self.is_model_valid(base_estimator, X_subset, y_subset)): self.n_skips_invalid_model_ += 1 continue # residuals of all data for current random sample model y_pred = base_estimator.predict(X) residuals_subset = loss_function(y, y_pred) # classify data into inliers and outliers inlier_mask_subset = residuals_subset < residual_threshold n_inliers_subset = np.sum(inlier_mask_subset) # less inliers -> skip current random sample if n_inliers_subset < n_inliers_best: self.n_skips_no_inliers_ += 1 continue # extract inlier data set inlier_idxs_subset = sample_idxs[inlier_mask_subset] X_inlier_subset = X[inlier_idxs_subset] y_inlier_subset = y[inlier_idxs_subset] # score of inlier data set score_subset = base_estimator.score(X_inlier_subset, y_inlier_subset) # same number of inliers but worse score -> skip current random # sample if (n_inliers_subset == n_inliers_best and score_subset < score_best): continue # save current random sample as best sample n_inliers_best = n_inliers_subset score_best = score_subset inlier_mask_best = inlier_mask_subset X_inlier_best = X_inlier_subset y_inlier_best = y_inlier_subset inlier_best_idxs_subset = inlier_idxs_subset max_trials = min( max_trials, _dynamic_max_trials(n_inliers_best, n_samples, min_samples, self.stop_probability)) # break if sufficient number of inliers or score is reached if n_inliers_best >= self.stop_n_inliers or \ score_best >= self.stop_score: break # if none of the iterations met the required criteria if inlier_mask_best is None: if ((self.n_skips_no_inliers_ + self.n_skips_invalid_data_ + self.n_skips_invalid_model_) > self.max_skips): raise ValueError( "RANSAC skipped more iterations than `max_skips` without" " finding a valid consensus set. Iterations were skipped" " because each randomly chosen sub-sample failed the" " passing criteria. See estimator attributes for" " diagnostics (n_skips*).") else: raise ValueError( "RANSAC could not find a valid consensus set. All" " `max_trials` iterations were skipped because each" " randomly chosen sub-sample failed the passing criteria." " See estimator attributes for diagnostics (n_skips*).") else: if (self.n_skips_no_inliers_ + self.n_skips_invalid_data_ + self.n_skips_invalid_model_) > self.max_skips: warnings.warn("RANSAC found a valid consensus set but exited" " early due to skipping more iterations than" " `max_skips`. See estimator attributes for" " diagnostics (n_skips*).", ConvergenceWarning) # estimate final model using all inliers if sample_weight is None: base_estimator.fit(X_inlier_best, y_inlier_best) else: base_estimator.fit( X_inlier_best, y_inlier_best, sample_weight=sample_weight[inlier_best_idxs_subset]) self.estimator_ = base_estimator self.inlier_mask_ = inlier_mask_best return self def predict(self, X): """Predict using the estimated model. This is a wrapper for `estimator_.predict(X)`. Parameters ---------- X : numpy array of shape [n_samples, n_features] Returns ------- y : array, shape = [n_samples] or [n_samples, n_targets] Returns predicted values. """ check_is_fitted(self) return self.estimator_.predict(X) def score(self, X, y): """Returns the score of the prediction. This is a wrapper for `estimator_.score(X, y)`. Parameters ---------- X : numpy array or sparse matrix of shape [n_samples, n_features] Training data. y : array, shape = [n_samples] or [n_samples, n_targets] Target values. Returns ------- z : float Score of the prediction. """ check_is_fitted(self) return self.estimator_.score(X, y) def _more_tags(self): return { '_xfail_checks': { 'check_sample_weights_invariance': 'zero sample_weight is not equivalent to removing samples', } }