import numpy as np
import scipy.sparse as sp
from scipy import linalg
from itertools import product

import pytest

from sklearn.utils.testing import assert_almost_equal
from sklearn.utils.testing import assert_array_almost_equal
from sklearn.utils.testing import assert_equal
from sklearn.utils.testing import assert_array_equal
from sklearn.utils.testing import assert_greater
from sklearn.utils.testing import assert_raises
from sklearn.utils.testing import assert_raise_message
from sklearn.utils.testing import assert_raises_regex
from sklearn.utils.testing import ignore_warnings
from sklearn.utils.testing import assert_warns

from sklearn.exceptions import ConvergenceWarning

from sklearn import datasets
from sklearn.metrics import mean_squared_error
from sklearn.metrics import make_scorer
from sklearn.metrics import get_scorer

from sklearn.linear_model.base import LinearRegression
from sklearn.linear_model.ridge import ridge_regression
from sklearn.linear_model.ridge import Ridge
from sklearn.linear_model.ridge import _RidgeGCV
from sklearn.linear_model.ridge import RidgeCV
from sklearn.linear_model.ridge import RidgeClassifier
from sklearn.linear_model.ridge import RidgeClassifierCV
from sklearn.linear_model.ridge import _solve_cholesky
from sklearn.linear_model.ridge import _solve_cholesky_kernel
from sklearn.datasets import make_regression

from sklearn.model_selection import GridSearchCV
from sklearn.model_selection import KFold

from sklearn.utils import check_random_state
from sklearn.datasets import make_multilabel_classification

diabetes = datasets.load_diabetes()
X_diabetes, y_diabetes = diabetes.data, diabetes.target
ind = np.arange(X_diabetes.shape[0])
rng = np.random.RandomState(0)
rng.shuffle(ind)
ind = ind[:200]
X_diabetes, y_diabetes = X_diabetes[ind], y_diabetes[ind]

iris = datasets.load_iris()

X_iris = sp.csr_matrix(iris.data)
y_iris = iris.target


DENSE_FILTER = lambda X: X
SPARSE_FILTER = lambda X: sp.csr_matrix(X)


@pytest.mark.parametrize('solver',
                         ("svd", "sparse_cg", "cholesky", "lsqr", "sag"))
def test_ridge(solver):
    # Ridge regression convergence test using score
    # TODO: for this test to be robust, we should use a dataset instead
    # of np.random.
    rng = np.random.RandomState(0)
    alpha = 1.0

    # With more samples than features
    n_samples, n_features = 6, 5
    y = rng.randn(n_samples)
    X = rng.randn(n_samples, n_features)

    ridge = Ridge(alpha=alpha, solver=solver)
    ridge.fit(X, y)
    assert_equal(ridge.coef_.shape, (X.shape[1], ))
    assert_greater(ridge.score(X, y), 0.47)

    if solver in ("cholesky", "sag"):
        # Currently the only solvers to support sample_weight.
        ridge.fit(X, y, sample_weight=np.ones(n_samples))
        assert_greater(ridge.score(X, y), 0.47)

    # With more features than samples
    n_samples, n_features = 5, 10
    y = rng.randn(n_samples)
    X = rng.randn(n_samples, n_features)
    ridge = Ridge(alpha=alpha, solver=solver)
    ridge.fit(X, y)
    assert_greater(ridge.score(X, y), .9)

    if solver in ("cholesky", "sag"):
        # Currently the only solvers to support sample_weight.
        ridge.fit(X, y, sample_weight=np.ones(n_samples))
        assert_greater(ridge.score(X, y), 0.9)


def test_primal_dual_relationship():
    y = y_diabetes.reshape(-1, 1)
    coef = _solve_cholesky(X_diabetes, y, alpha=[1e-2])
    K = np.dot(X_diabetes, X_diabetes.T)
    dual_coef = _solve_cholesky_kernel(K, y, alpha=[1e-2])
    coef2 = np.dot(X_diabetes.T, dual_coef).T
    assert_array_almost_equal(coef, coef2)


def test_ridge_singular():
    # test on a singular matrix
    rng = np.random.RandomState(0)
    n_samples, n_features = 6, 6
    y = rng.randn(n_samples // 2)
    y = np.concatenate((y, y))
    X = rng.randn(n_samples // 2, n_features)
    X = np.concatenate((X, X), axis=0)

    ridge = Ridge(alpha=0)
    ridge.fit(X, y)
    assert_greater(ridge.score(X, y), 0.9)


def test_ridge_regression_sample_weights():
    rng = np.random.RandomState(0)

    for solver in ("cholesky", ):
        for n_samples, n_features in ((6, 5), (5, 10)):
            for alpha in (1.0, 1e-2):
                y = rng.randn(n_samples)
                X = rng.randn(n_samples, n_features)
                sample_weight = 1.0 + rng.rand(n_samples)

                coefs = ridge_regression(X, y,
                                         alpha=alpha,
                                         sample_weight=sample_weight,
                                         solver=solver)

                # Sample weight can be implemented via a simple rescaling
                # for the square loss.
                coefs2 = ridge_regression(
                    X * np.sqrt(sample_weight)[:, np.newaxis],
                    y * np.sqrt(sample_weight),
                    alpha=alpha, solver=solver)
                assert_array_almost_equal(coefs, coefs2)


def test_ridge_regression_convergence_fail():
    rng = np.random.RandomState(0)
    y = rng.randn(5)
    X = rng.randn(5, 10)

    assert_warns(ConvergenceWarning, ridge_regression,
                 X, y, alpha=1.0, solver="sparse_cg",
                 tol=0., max_iter=None, verbose=1)


def test_ridge_sample_weights():
    # TODO: loop over sparse data as well
    # Note: parametrizing this test with pytest results in failed
    #       assertions, meaning that is is not extremely robust

    rng = np.random.RandomState(0)
    param_grid = product((1.0, 1e-2), (True, False),
                         ('svd', 'cholesky', 'lsqr', 'sparse_cg'))

    for n_samples, n_features in ((6, 5), (5, 10)):

        y = rng.randn(n_samples)
        X = rng.randn(n_samples, n_features)
        sample_weight = 1.0 + rng.rand(n_samples)

        for (alpha, intercept, solver) in param_grid:

            # Ridge with explicit sample_weight
            est = Ridge(alpha=alpha, fit_intercept=intercept,
                        solver=solver, tol=1e-6)
            est.fit(X, y, sample_weight=sample_weight)
            coefs = est.coef_
            inter = est.intercept_

            # Closed form of the weighted regularized least square
            # theta = (X^T W X + alpha I)^(-1) * X^T W y
            W = np.diag(sample_weight)
            if intercept is False:
                X_aug = X
                I = np.eye(n_features)
            else:
                dummy_column = np.ones(shape=(n_samples, 1))
                X_aug = np.concatenate((dummy_column, X), axis=1)
                I = np.eye(n_features + 1)
                I[0, 0] = 0

            cf_coefs = linalg.solve(X_aug.T.dot(W).dot(X_aug) + alpha * I,
                                    X_aug.T.dot(W).dot(y))

            if intercept is False:
                assert_array_almost_equal(coefs, cf_coefs)
            else:
                assert_array_almost_equal(coefs, cf_coefs[1:])
                assert_almost_equal(inter, cf_coefs[0])


def test_ridge_shapes():
    # Test shape of coef_ and intercept_
    rng = np.random.RandomState(0)
    n_samples, n_features = 5, 10
    X = rng.randn(n_samples, n_features)
    y = rng.randn(n_samples)
    Y1 = y[:, np.newaxis]
    Y = np.c_[y, 1 + y]

    ridge = Ridge()

    ridge.fit(X, y)
    assert_equal(ridge.coef_.shape, (n_features,))
    assert_equal(ridge.intercept_.shape, ())

    ridge.fit(X, Y1)
    assert_equal(ridge.coef_.shape, (1, n_features))
    assert_equal(ridge.intercept_.shape, (1, ))

    ridge.fit(X, Y)
    assert_equal(ridge.coef_.shape, (2, n_features))
    assert_equal(ridge.intercept_.shape, (2, ))


def test_ridge_intercept():
    # Test intercept with multiple targets GH issue #708
    rng = np.random.RandomState(0)
    n_samples, n_features = 5, 10
    X = rng.randn(n_samples, n_features)
    y = rng.randn(n_samples)
    Y = np.c_[y, 1. + y]

    ridge = Ridge()

    ridge.fit(X, y)
    intercept = ridge.intercept_

    ridge.fit(X, Y)
    assert_almost_equal(ridge.intercept_[0], intercept)
    assert_almost_equal(ridge.intercept_[1], intercept + 1.)


def test_toy_ridge_object():
    # Test BayesianRegression ridge classifier
    # TODO: test also n_samples > n_features
    X = np.array([[1], [2]])
    Y = np.array([1, 2])
    reg = Ridge(alpha=0.0)
    reg.fit(X, Y)
    X_test = [[1], [2], [3], [4]]
    assert_almost_equal(reg.predict(X_test), [1., 2, 3, 4])

    assert_equal(len(reg.coef_.shape), 1)
    assert_equal(type(reg.intercept_), np.float64)

    Y = np.vstack((Y, Y)).T

    reg.fit(X, Y)
    X_test = [[1], [2], [3], [4]]

    assert_equal(len(reg.coef_.shape), 2)
    assert_equal(type(reg.intercept_), np.ndarray)


def test_ridge_vs_lstsq():
    # On alpha=0., Ridge and OLS yield the same solution.

    rng = np.random.RandomState(0)
    # we need more samples than features
    n_samples, n_features = 5, 4
    y = rng.randn(n_samples)
    X = rng.randn(n_samples, n_features)

    ridge = Ridge(alpha=0., fit_intercept=False)
    ols = LinearRegression(fit_intercept=False)

    ridge.fit(X, y)
    ols.fit(X, y)
    assert_almost_equal(ridge.coef_, ols.coef_)

    ridge.fit(X, y)
    ols.fit(X, y)
    assert_almost_equal(ridge.coef_, ols.coef_)


def test_ridge_individual_penalties():
    # Tests the ridge object using individual penalties

    rng = np.random.RandomState(42)

    n_samples, n_features, n_targets = 20, 10, 5
    X = rng.randn(n_samples, n_features)
    y = rng.randn(n_samples, n_targets)

    penalties = np.arange(n_targets)

    coef_cholesky = np.array([
        Ridge(alpha=alpha, solver="cholesky").fit(X, target).coef_
        for alpha, target in zip(penalties, y.T)])

    coefs_indiv_pen = [
        Ridge(alpha=penalties, solver=solver, tol=1e-8).fit(X, y).coef_
        for solver in ['svd', 'sparse_cg', 'lsqr', 'cholesky', 'sag', 'saga']]
    for coef_indiv_pen in coefs_indiv_pen:
        assert_array_almost_equal(coef_cholesky, coef_indiv_pen)

    # Test error is raised when number of targets and penalties do not match.
    ridge = Ridge(alpha=penalties[:-1])
    assert_raises(ValueError, ridge.fit, X, y)


def _test_ridge_loo(filter_):
    # test that can work with both dense or sparse matrices
    n_samples = X_diabetes.shape[0]

    ret = []

    fit_intercept = filter_ == DENSE_FILTER
    if fit_intercept:
        X_diabetes_ = X_diabetes - X_diabetes.mean(0)
    else:
        X_diabetes_ = X_diabetes
    ridge_gcv = _RidgeGCV(fit_intercept=fit_intercept)
    ridge = Ridge(alpha=1.0, fit_intercept=fit_intercept)

    # because fit_intercept is applied

    # generalized cross-validation (efficient leave-one-out)
    decomp = ridge_gcv._pre_compute(X_diabetes_, y_diabetes, fit_intercept)
    errors, c = ridge_gcv._errors(1.0, y_diabetes, *decomp)
    values, c = ridge_gcv._values(1.0, y_diabetes, *decomp)

    # brute-force leave-one-out: remove one example at a time
    errors2 = []
    values2 = []
    for i in range(n_samples):
        sel = np.arange(n_samples) != i
        X_new = X_diabetes_[sel]
        y_new = y_diabetes[sel]
        ridge.fit(X_new, y_new)
        value = ridge.predict([X_diabetes_[i]])[0]
        error = (y_diabetes[i] - value) ** 2
        errors2.append(error)
        values2.append(value)

    # check that efficient and brute-force LOO give same results
    assert_almost_equal(errors, errors2)
    assert_almost_equal(values, values2)

    # generalized cross-validation (efficient leave-one-out,
    # SVD variation)
    decomp = ridge_gcv._pre_compute_svd(X_diabetes_, y_diabetes, fit_intercept)
    errors3, c = ridge_gcv._errors_svd(ridge.alpha, y_diabetes, *decomp)
    values3, c = ridge_gcv._values_svd(ridge.alpha, y_diabetes, *decomp)

    # check that efficient and SVD efficient LOO give same results
    assert_almost_equal(errors, errors3)
    assert_almost_equal(values, values3)

    # check best alpha
    ridge_gcv.fit(filter_(X_diabetes), y_diabetes)
    alpha_ = ridge_gcv.alpha_
    ret.append(alpha_)

    # check that we get same best alpha with custom loss_func
    f = ignore_warnings
    scoring = make_scorer(mean_squared_error, greater_is_better=False)
    ridge_gcv2 = RidgeCV(fit_intercept=False, scoring=scoring)
    f(ridge_gcv2.fit)(filter_(X_diabetes), y_diabetes)
    assert_equal(ridge_gcv2.alpha_, alpha_)

    # check that we get same best alpha with custom score_func
    func = lambda x, y: -mean_squared_error(x, y)
    scoring = make_scorer(func)
    ridge_gcv3 = RidgeCV(fit_intercept=False, scoring=scoring)
    f(ridge_gcv3.fit)(filter_(X_diabetes), y_diabetes)
    assert_equal(ridge_gcv3.alpha_, alpha_)

    # check that we get same best alpha with a scorer
    scorer = get_scorer('neg_mean_squared_error')
    ridge_gcv4 = RidgeCV(fit_intercept=False, scoring=scorer)
    ridge_gcv4.fit(filter_(X_diabetes), y_diabetes)
    assert_equal(ridge_gcv4.alpha_, alpha_)

    # check that we get same best alpha with sample weights
    ridge_gcv.fit(filter_(X_diabetes), y_diabetes,
                  sample_weight=np.ones(n_samples))
    assert_equal(ridge_gcv.alpha_, alpha_)

    # simulate several responses
    Y = np.vstack((y_diabetes, y_diabetes)).T

    ridge_gcv.fit(filter_(X_diabetes), Y)
    Y_pred = ridge_gcv.predict(filter_(X_diabetes))
    ridge_gcv.fit(filter_(X_diabetes), y_diabetes)
    y_pred = ridge_gcv.predict(filter_(X_diabetes))

    assert_array_almost_equal(np.vstack((y_pred, y_pred)).T,
                              Y_pred, decimal=5)

    return ret


def _test_ridge_cv_normalize(filter_):
    ridge_cv = RidgeCV(normalize=True, cv=3)
    ridge_cv.fit(filter_(10. * X_diabetes), y_diabetes)

    gs = GridSearchCV(Ridge(normalize=True), cv=3,
                      param_grid={'alpha': ridge_cv.alphas})
    gs.fit(filter_(10. * X_diabetes), y_diabetes)
    assert_equal(gs.best_estimator_.alpha, ridge_cv.alpha_)


def _test_ridge_cv(filter_):
    ridge_cv = RidgeCV()
    ridge_cv.fit(filter_(X_diabetes), y_diabetes)
    ridge_cv.predict(filter_(X_diabetes))

    assert_equal(len(ridge_cv.coef_.shape), 1)
    assert_equal(type(ridge_cv.intercept_), np.float64)

    cv = KFold(5)
    ridge_cv.set_params(cv=cv)
    ridge_cv.fit(filter_(X_diabetes), y_diabetes)
    ridge_cv.predict(filter_(X_diabetes))

    assert_equal(len(ridge_cv.coef_.shape), 1)
    assert_equal(type(ridge_cv.intercept_), np.float64)


def _test_ridge_diabetes(filter_):
    ridge = Ridge(fit_intercept=False)
    ridge.fit(filter_(X_diabetes), y_diabetes)
    return np.round(ridge.score(filter_(X_diabetes), y_diabetes), 5)


def _test_multi_ridge_diabetes(filter_):
    # simulate several responses
    Y = np.vstack((y_diabetes, y_diabetes)).T
    n_features = X_diabetes.shape[1]

    ridge = Ridge(fit_intercept=False)
    ridge.fit(filter_(X_diabetes), Y)
    assert_equal(ridge.coef_.shape, (2, n_features))
    Y_pred = ridge.predict(filter_(X_diabetes))
    ridge.fit(filter_(X_diabetes), y_diabetes)
    y_pred = ridge.predict(filter_(X_diabetes))
    assert_array_almost_equal(np.vstack((y_pred, y_pred)).T,
                              Y_pred, decimal=3)


def _test_ridge_classifiers(filter_):
    n_classes = np.unique(y_iris).shape[0]
    n_features = X_iris.shape[1]
    for reg in (RidgeClassifier(), RidgeClassifierCV()):
        reg.fit(filter_(X_iris), y_iris)
        assert_equal(reg.coef_.shape, (n_classes, n_features))
        y_pred = reg.predict(filter_(X_iris))
        assert_greater(np.mean(y_iris == y_pred), .79)

    cv = KFold(5)
    reg = RidgeClassifierCV(cv=cv)
    reg.fit(filter_(X_iris), y_iris)
    y_pred = reg.predict(filter_(X_iris))
    assert np.mean(y_iris == y_pred) >= 0.8


def _test_tolerance(filter_):
    ridge = Ridge(tol=1e-5, fit_intercept=False)
    ridge.fit(filter_(X_diabetes), y_diabetes)
    score = ridge.score(filter_(X_diabetes), y_diabetes)

    ridge2 = Ridge(tol=1e-3, fit_intercept=False)
    ridge2.fit(filter_(X_diabetes), y_diabetes)
    score2 = ridge2.score(filter_(X_diabetes), y_diabetes)

    assert score >= score2


def check_dense_sparse(test_func):
    # test dense matrix
    ret_dense = test_func(DENSE_FILTER)
    # test sparse matrix
    ret_sparse = test_func(SPARSE_FILTER)
    # test that the outputs are the same
    if ret_dense is not None and ret_sparse is not None:
        assert_array_almost_equal(ret_dense, ret_sparse, decimal=3)


@pytest.mark.filterwarnings('ignore: The default of the `iid`')  # 0.22
@pytest.mark.filterwarnings('ignore: You should specify a value')  # 0.22
@pytest.mark.parametrize(
        'test_func',
        (_test_ridge_loo, _test_ridge_cv, _test_ridge_cv_normalize,
         _test_ridge_diabetes, _test_multi_ridge_diabetes,
         _test_ridge_classifiers, _test_tolerance))
def test_dense_sparse(test_func):
    check_dense_sparse(test_func)


def test_ridge_cv_sparse_svd():
    X = sp.csr_matrix(X_diabetes)
    ridge = RidgeCV(gcv_mode="svd")
    assert_raises(TypeError, ridge.fit, X)


def test_ridge_sparse_svd():
    X = sp.csc_matrix(rng.rand(100, 10))
    y = rng.rand(100)
    ridge = Ridge(solver='svd', fit_intercept=False)
    assert_raises(TypeError, ridge.fit, X, y)


def test_class_weights():
    # Test class weights.
    X = np.array([[-1.0, -1.0], [-1.0, 0], [-.8, -1.0],
                  [1.0, 1.0], [1.0, 0.0]])
    y = [1, 1, 1, -1, -1]

    reg = RidgeClassifier(class_weight=None)
    reg.fit(X, y)
    assert_array_equal(reg.predict([[0.2, -1.0]]), np.array([1]))

    # we give a small weights to class 1
    reg = RidgeClassifier(class_weight={1: 0.001})
    reg.fit(X, y)

    # now the hyperplane should rotate clock-wise and
    # the prediction on this point should shift
    assert_array_equal(reg.predict([[0.2, -1.0]]), np.array([-1]))

    # check if class_weight = 'balanced' can handle negative labels.
    reg = RidgeClassifier(class_weight='balanced')
    reg.fit(X, y)
    assert_array_equal(reg.predict([[0.2, -1.0]]), np.array([1]))

    # class_weight = 'balanced', and class_weight = None should return
    # same values when y has equal number of all labels
    X = np.array([[-1.0, -1.0], [-1.0, 0], [-.8, -1.0], [1.0, 1.0]])
    y = [1, 1, -1, -1]
    reg = RidgeClassifier(class_weight=None)
    reg.fit(X, y)
    rega = RidgeClassifier(class_weight='balanced')
    rega.fit(X, y)
    assert_equal(len(rega.classes_), 2)
    assert_array_almost_equal(reg.coef_, rega.coef_)
    assert_array_almost_equal(reg.intercept_, rega.intercept_)


@pytest.mark.filterwarnings('ignore: You should specify a value')  # 0.22
@pytest.mark.parametrize('reg', (RidgeClassifier, RidgeClassifierCV))
def test_class_weight_vs_sample_weight(reg):
    """Check class_weights resemble sample_weights behavior."""

    # Iris is balanced, so no effect expected for using 'balanced' weights
    reg1 = reg()
    reg1.fit(iris.data, iris.target)
    reg2 = reg(class_weight='balanced')
    reg2.fit(iris.data, iris.target)
    assert_almost_equal(reg1.coef_, reg2.coef_)

    # Inflate importance of class 1, check against user-defined weights
    sample_weight = np.ones(iris.target.shape)
    sample_weight[iris.target == 1] *= 100
    class_weight = {0: 1., 1: 100., 2: 1.}
    reg1 = reg()
    reg1.fit(iris.data, iris.target, sample_weight)
    reg2 = reg(class_weight=class_weight)
    reg2.fit(iris.data, iris.target)
    assert_almost_equal(reg1.coef_, reg2.coef_)

    # Check that sample_weight and class_weight are multiplicative
    reg1 = reg()
    reg1.fit(iris.data, iris.target, sample_weight ** 2)
    reg2 = reg(class_weight=class_weight)
    reg2.fit(iris.data, iris.target, sample_weight)
    assert_almost_equal(reg1.coef_, reg2.coef_)


@pytest.mark.filterwarnings('ignore: You should specify a value')  # 0.22
def test_class_weights_cv():
    # Test class weights for cross validated ridge classifier.
    X = np.array([[-1.0, -1.0], [-1.0, 0], [-.8, -1.0],
                  [1.0, 1.0], [1.0, 0.0]])
    y = [1, 1, 1, -1, -1]

    reg = RidgeClassifierCV(class_weight=None, alphas=[.01, .1, 1])
    reg.fit(X, y)

    # we give a small weights to class 1
    reg = RidgeClassifierCV(class_weight={1: 0.001}, alphas=[.01, .1, 1, 10])
    reg.fit(X, y)

    assert_array_equal(reg.predict([[-.2, 2]]), np.array([-1]))


@pytest.mark.filterwarnings('ignore: You should specify a value')  # 0.22
def test_ridgecv_store_cv_values():
    rng = np.random.RandomState(42)

    n_samples = 8
    n_features = 5
    x = rng.randn(n_samples, n_features)
    alphas = [1e-1, 1e0, 1e1]
    n_alphas = len(alphas)

    r = RidgeCV(alphas=alphas, cv=None, store_cv_values=True)

    # with len(y.shape) == 1
    y = rng.randn(n_samples)
    r.fit(x, y)
    assert r.cv_values_.shape == (n_samples, n_alphas)

    # with len(y.shape) == 2
    n_targets = 3
    y = rng.randn(n_samples, n_targets)
    r.fit(x, y)
    assert r.cv_values_.shape == (n_samples, n_targets, n_alphas)


@pytest.mark.filterwarnings('ignore: You should specify a value')  # 0.22
def test_ridge_classifier_cv_store_cv_values():
    x = np.array([[-1.0, -1.0], [-1.0, 0], [-.8, -1.0],
                  [1.0, 1.0], [1.0, 0.0]])
    y = np.array([1, 1, 1, -1, -1])

    n_samples = x.shape[0]
    alphas = [1e-1, 1e0, 1e1]
    n_alphas = len(alphas)

    r = RidgeClassifierCV(alphas=alphas, cv=None, store_cv_values=True)

    # with len(y.shape) == 1
    n_targets = 1
    r.fit(x, y)
    assert r.cv_values_.shape == (n_samples, n_targets, n_alphas)

    # with len(y.shape) == 2
    y = np.array([[1, 1, 1, -1, -1],
                  [1, -1, 1, -1, 1],
                  [-1, -1, 1, -1, -1]]).transpose()
    n_targets = y.shape[1]
    r.fit(x, y)
    assert r.cv_values_.shape == (n_samples, n_targets, n_alphas)


@pytest.mark.filterwarnings('ignore: The default of the `iid`')  # 0.22
def test_ridgecv_sample_weight():
    rng = np.random.RandomState(0)
    alphas = (0.1, 1.0, 10.0)

    # There are different algorithms for n_samples > n_features
    # and the opposite, so test them both.
    for n_samples, n_features in ((6, 5), (5, 10)):
        y = rng.randn(n_samples)
        X = rng.randn(n_samples, n_features)
        sample_weight = 1.0 + rng.rand(n_samples)

        cv = KFold(5)
        ridgecv = RidgeCV(alphas=alphas, cv=cv)
        ridgecv.fit(X, y, sample_weight=sample_weight)

        # Check using GridSearchCV directly
        parameters = {'alpha': alphas}
        gs = GridSearchCV(Ridge(), parameters, cv=cv)
        gs.fit(X, y, sample_weight=sample_weight)

        assert ridgecv.alpha_ == gs.best_estimator_.alpha
        assert_array_almost_equal(ridgecv.coef_, gs.best_estimator_.coef_)


def test_raises_value_error_if_sample_weights_greater_than_1d():
    # Sample weights must be either scalar or 1D

    n_sampless = [2, 3]
    n_featuress = [3, 2]

    rng = np.random.RandomState(42)

    for n_samples, n_features in zip(n_sampless, n_featuress):
        X = rng.randn(n_samples, n_features)
        y = rng.randn(n_samples)
        sample_weights_OK = rng.randn(n_samples) ** 2 + 1
        sample_weights_OK_1 = 1.
        sample_weights_OK_2 = 2.
        sample_weights_not_OK = sample_weights_OK[:, np.newaxis]
        sample_weights_not_OK_2 = sample_weights_OK[np.newaxis, :]

        ridge = Ridge(alpha=1)

        # make sure the "OK" sample weights actually work
        ridge.fit(X, y, sample_weights_OK)
        ridge.fit(X, y, sample_weights_OK_1)
        ridge.fit(X, y, sample_weights_OK_2)

        def fit_ridge_not_ok():
            ridge.fit(X, y, sample_weights_not_OK)

        def fit_ridge_not_ok_2():
            ridge.fit(X, y, sample_weights_not_OK_2)

        assert_raise_message(ValueError,
                             "Sample weights must be 1D array or scalar",
                             fit_ridge_not_ok)

        assert_raise_message(ValueError,
                             "Sample weights must be 1D array or scalar",
                             fit_ridge_not_ok_2)


def test_sparse_design_with_sample_weights():
    # Sample weights must work with sparse matrices

    n_sampless = [2, 3]
    n_featuress = [3, 2]

    rng = np.random.RandomState(42)

    sparse_matrix_converters = [sp.coo_matrix,
                                sp.csr_matrix,
                                sp.csc_matrix,
                                sp.lil_matrix,
                                sp.dok_matrix
                                ]

    sparse_ridge = Ridge(alpha=1., fit_intercept=False)
    dense_ridge = Ridge(alpha=1., fit_intercept=False)

    for n_samples, n_features in zip(n_sampless, n_featuress):
        X = rng.randn(n_samples, n_features)
        y = rng.randn(n_samples)
        sample_weights = rng.randn(n_samples) ** 2 + 1
        for sparse_converter in sparse_matrix_converters:
            X_sparse = sparse_converter(X)
            sparse_ridge.fit(X_sparse, y, sample_weight=sample_weights)
            dense_ridge.fit(X, y, sample_weight=sample_weights)

            assert_array_almost_equal(sparse_ridge.coef_, dense_ridge.coef_,
                                      decimal=6)


@pytest.mark.filterwarnings('ignore: You should specify a value')  # 0.22
def test_ridgecv_int_alphas():
    X = np.array([[-1.0, -1.0], [-1.0, 0], [-.8, -1.0],
                  [1.0, 1.0], [1.0, 0.0]])
    y = [1, 1, 1, -1, -1]

    # Integers
    ridge = RidgeCV(alphas=(1, 10, 100))
    ridge.fit(X, y)


@pytest.mark.filterwarnings('ignore: You should specify a value')  # 0.22
def test_ridgecv_negative_alphas():
    X = np.array([[-1.0, -1.0], [-1.0, 0], [-.8, -1.0],
                  [1.0, 1.0], [1.0, 0.0]])
    y = [1, 1, 1, -1, -1]

    # Negative integers
    ridge = RidgeCV(alphas=(-1, -10, -100))
    assert_raises_regex(ValueError,
                        "alphas cannot be negative.",
                        ridge.fit, X, y)

    # Negative floats
    ridge = RidgeCV(alphas=(-0.1, -1.0, -10.0))
    assert_raises_regex(ValueError,
                        "alphas cannot be negative.",
                        ridge.fit, X, y)


def test_raises_value_error_if_solver_not_supported():
    # Tests whether a ValueError is raised if a non-identified solver
    # is passed to ridge_regression

    wrong_solver = "This is not a solver (MagritteSolveCV QuantumBitcoin)"

    exception = ValueError
    message = "Solver %s not understood" % wrong_solver

    def func():
        X = np.eye(3)
        y = np.ones(3)
        ridge_regression(X, y, alpha=1., solver=wrong_solver)

    assert_raise_message(exception, message, func)


def test_sparse_cg_max_iter():
    reg = Ridge(solver="sparse_cg", max_iter=1)
    reg.fit(X_diabetes, y_diabetes)
    assert_equal(reg.coef_.shape[0], X_diabetes.shape[1])


@ignore_warnings
def test_n_iter():
    # Test that self.n_iter_ is correct.
    n_targets = 2
    X, y = X_diabetes, y_diabetes
    y_n = np.tile(y, (n_targets, 1)).T

    for max_iter in range(1, 4):
        for solver in ('sag', 'saga', 'lsqr'):
            reg = Ridge(solver=solver, max_iter=max_iter, tol=1e-12)
            reg.fit(X, y_n)
            assert_array_equal(reg.n_iter_, np.tile(max_iter, n_targets))

    for solver in ('sparse_cg', 'svd', 'cholesky'):
        reg = Ridge(solver=solver, max_iter=1, tol=1e-1)
        reg.fit(X, y_n)
        assert_equal(reg.n_iter_, None)


def test_ridge_fit_intercept_sparse():
    X, y = make_regression(n_samples=1000, n_features=2, n_informative=2,
                           bias=10., random_state=42)
    X_csr = sp.csr_matrix(X)

    for solver in ['saga', 'sag']:
        dense = Ridge(alpha=1., tol=1.e-15, solver=solver, fit_intercept=True)
        sparse = Ridge(alpha=1., tol=1.e-15, solver=solver, fit_intercept=True)
        dense.fit(X, y)
        sparse.fit(X_csr, y)
        assert_almost_equal(dense.intercept_, sparse.intercept_)
        assert_array_almost_equal(dense.coef_, sparse.coef_)

    # test the solver switch and the corresponding warning
    sparse = Ridge(alpha=1., tol=1.e-15, solver='lsqr', fit_intercept=True)
    assert_warns(UserWarning, sparse.fit, X_csr, y)
    assert_almost_equal(dense.intercept_, sparse.intercept_)
    assert_array_almost_equal(dense.coef_, sparse.coef_)


def test_errors_and_values_helper():
    ridgecv = _RidgeGCV()
    rng = check_random_state(42)
    alpha = 1.
    n = 5
    y = rng.randn(n)
    v = rng.randn(n)
    Q = rng.randn(len(v), len(v))
    QT_y = Q.T.dot(y)
    G_diag, c = ridgecv._errors_and_values_helper(alpha, y, v, Q, QT_y)

    # test that helper function behaves as expected
    out, c_ = ridgecv._errors(alpha, y, v, Q, QT_y)
    np.testing.assert_array_equal(out, (c / G_diag) ** 2)
    np.testing.assert_array_equal(c, c)

    out, c_ = ridgecv._values(alpha, y, v, Q, QT_y)
    np.testing.assert_array_equal(out, y - (c / G_diag))
    np.testing.assert_array_equal(c_, c)


def test_errors_and_values_svd_helper():
    ridgecv = _RidgeGCV()
    rng = check_random_state(42)
    alpha = 1.
    for n, p in zip((5, 10), (12, 6)):
        y = rng.randn(n)
        v = rng.randn(p)
        U = rng.randn(n, p)
        UT_y = U.T.dot(y)
        G_diag, c = ridgecv._errors_and_values_svd_helper(alpha, y, v, U, UT_y)

        # test that helper function behaves as expected
        out, c_ = ridgecv._errors_svd(alpha, y, v, U, UT_y)
        np.testing.assert_array_equal(out, (c / G_diag) ** 2)
        np.testing.assert_array_equal(c, c)

        out, c_ = ridgecv._values_svd(alpha, y, v, U, UT_y)
        np.testing.assert_array_equal(out, y - (c / G_diag))
        np.testing.assert_array_equal(c_, c)


def test_ridge_classifier_no_support_multilabel():
    X, y = make_multilabel_classification(n_samples=10, random_state=0)
    assert_raises(ValueError, RidgeClassifier().fit, X, y)


def test_dtype_match():
    rng = np.random.RandomState(0)
    alpha = 1.0

    n_samples, n_features = 6, 5
    X_64 = rng.randn(n_samples, n_features)
    y_64 = rng.randn(n_samples)
    X_32 = X_64.astype(np.float32)
    y_32 = y_64.astype(np.float32)

    solvers = ["svd", "sparse_cg", "cholesky", "lsqr"]
    for solver in solvers:

        # Check type consistency 32bits
        ridge_32 = Ridge(alpha=alpha, solver=solver)
        ridge_32.fit(X_32, y_32)
        coef_32 = ridge_32.coef_

        # Check type consistency 64 bits
        ridge_64 = Ridge(alpha=alpha, solver=solver)
        ridge_64.fit(X_64, y_64)
        coef_64 = ridge_64.coef_

        # Do the actual checks at once for easier debug
        assert coef_32.dtype == X_32.dtype
        assert coef_64.dtype == X_64.dtype
        assert ridge_32.predict(X_32).dtype == X_32.dtype
        assert ridge_64.predict(X_64).dtype == X_64.dtype
        assert_almost_equal(ridge_32.coef_, ridge_64.coef_, decimal=5)


def test_dtype_match_cholesky():
    # Test different alphas in cholesky solver to ensure full coverage.
    # This test is separated from test_dtype_match for clarity.
    rng = np.random.RandomState(0)
    alpha = (1.0, 0.5)

    n_samples, n_features, n_target = 6, 7, 2
    X_64 = rng.randn(n_samples, n_features)
    y_64 = rng.randn(n_samples, n_target)
    X_32 = X_64.astype(np.float32)
    y_32 = y_64.astype(np.float32)

    # Check type consistency 32bits
    ridge_32 = Ridge(alpha=alpha, solver='cholesky')
    ridge_32.fit(X_32, y_32)
    coef_32 = ridge_32.coef_

    # Check type consistency 64 bits
    ridge_64 = Ridge(alpha=alpha, solver='cholesky')
    ridge_64.fit(X_64, y_64)
    coef_64 = ridge_64.coef_

    # Do all the checks at once, like this is easier to debug
    assert coef_32.dtype == X_32.dtype
    assert coef_64.dtype == X_64.dtype
    assert ridge_32.predict(X_32).dtype == X_32.dtype
    assert ridge_64.predict(X_64).dtype == X_64.dtype
    assert_almost_equal(ridge_32.coef_, ridge_64.coef_, decimal=5)