# flake8: noqa
"""
========================================
Release Highlights for scikit-learn 0.23
========================================

.. currentmodule:: sklearn

We are pleased to announce the release of scikit-learn 0.23! Many bug fixes
and improvements were added, as well as some new key features. We detail
below a few of the major features of this release. **For an exhaustive list of
all the changes**, please refer to the :ref:`release notes <changes_0_23>`.

To install the latest version (with pip)::

    pip install --upgrade scikit-learn

or with conda::

    conda install scikit-learn
"""

##############################################################################
# Generalized Linear Models, and Poisson loss for gradient boosting
# -----------------------------------------------------------------
# Long-awaited Generalized Linear Models with non-normal loss functions are now
# available. In particular, three new regressors were implemented:
# :class:`~sklearn.linear_model.PoissonRegressor`,
# :class:`~sklearn.linear_model.GammaRegressor`, and
# :class:`~sklearn.linear_model.TweedieRegressor`. The Poisson regressor can be
# used to model positive integer counts, or relative frequencies. Read more in
# the :ref:`User Guide <Generalized_linear_regression>`. Additionally,
# :class:`~sklearn.ensemble.HistGradientBoostingRegressor` supports a new
# 'poisson' loss as well.

import numpy as np
from sklearn.model_selection import train_test_split
from sklearn.linear_model import PoissonRegressor
from sklearn.experimental import enable_hist_gradient_boosting  # noqa
from sklearn.ensemble import HistGradientBoostingRegressor

n_samples, n_features = 1000, 20
rng = np.random.RandomState(0)
X = rng.randn(n_samples, n_features)
# positive integer target correlated with X[:, 5] with many zeros:
y = rng.poisson(lam=np.exp(X[:, 5]) / 2)
X_train, X_test, y_train, y_test = train_test_split(X, y, random_state=rng)
glm = PoissonRegressor()
gbdt = HistGradientBoostingRegressor(loss='poisson', learning_rate=.01)
glm.fit(X_train, y_train)
gbdt.fit(X_train, y_train)
print(glm.score(X_test, y_test))
print(gbdt.score(X_test, y_test))

##############################################################################
# Rich visual representation of estimators
# -----------------------------------------
# Estimators can now be visualized in notebooks by enabling the
# `display='diagram'` option. This is particularly useful to summarise the
# structure of pipelines and other composite estimators, with interactivity to
# provide detail.  Click on the example image below to expand Pipeline
# elements.  See :ref:`visualizing_composite_estimators` for how you can use
# this feature.

from sklearn import set_config
from sklearn.pipeline import make_pipeline
from sklearn.preprocessing import OneHotEncoder, StandardScaler
from sklearn.impute import SimpleImputer
from sklearn.compose import make_column_transformer
from sklearn.linear_model import LogisticRegression
set_config(display='diagram')

num_proc = make_pipeline(SimpleImputer(strategy='median'), StandardScaler())

cat_proc = make_pipeline(
    SimpleImputer(strategy='constant', fill_value='missing'),
    OneHotEncoder(handle_unknown='ignore'))

preprocessor = make_column_transformer((num_proc, ('feat1', 'feat3')),
                                       (cat_proc, ('feat0', 'feat2')))

clf = make_pipeline(preprocessor, LogisticRegression())
clf

##############################################################################
# Scalability and stability improvements to KMeans
# ------------------------------------------------
# The :class:`~sklearn.cluster.KMeans` estimator was entirely re-worked, and it
# is now significantly faster and more stable. In addition, the Elkan algorithm
# is now compatible with sparse matrices. The estimator uses OpenMP based
# parallelism instead of relying on joblib, so the `n_jobs` parameter has no
# effect anymore. For more details on how to control the number of threads,
# please refer to our :ref:`parallelism` notes.
import scipy
import numpy as np
from sklearn.model_selection import train_test_split
from sklearn.cluster import KMeans
from sklearn.datasets import make_blobs
from sklearn.metrics import completeness_score

rng = np.random.RandomState(0)
X, y = make_blobs(random_state=rng)
X = scipy.sparse.csr_matrix(X)
X_train, X_test, _, y_test = train_test_split(X, y, random_state=rng)
kmeans = KMeans(algorithm='elkan').fit(X_train)
print(completeness_score(kmeans.predict(X_test), y_test))

##############################################################################
# Improvements to the histogram-based Gradient Boosting estimators
# ----------------------------------------------------------------
# Various improvements were made to
# :class:`~sklearn.ensemble.HistGradientBoostingClassifier` and
# :class:`~sklearn.ensemble.HistGradientBoostingRegressor`. On top of the
# Poisson loss mentionned above, these estimators now support :ref:`sample
# weights <sw_hgbdt>`. Also, an automatic early-stopping criterion was added:
# early-stopping is enabled by default when the number of samples exceeds 10k.
# Finally, users can now define :ref:`monotonic constraints
# <monotonic_cst_gbdt>` to constrain the predictions based on the variations of
# specific features. In the following example, we construct a target that is
# generally positively correlated with the first feature, with some noise.
# Applying monotoinc constraints allows the prediction to capture the global
# effect of the first feature, instead of fitting the noise.
import numpy as np
from matplotlib import pyplot as plt
from sklearn.model_selection import train_test_split
from sklearn.inspection import plot_partial_dependence
from sklearn.experimental import enable_hist_gradient_boosting  # noqa
from sklearn.ensemble import HistGradientBoostingRegressor

n_samples = 500
rng = np.random.RandomState(0)
X = rng.randn(n_samples, 2)
noise = rng.normal(loc=0.0, scale=0.01, size=n_samples)
y = (5 * X[:, 0] + np.sin(10 * np.pi * X[:, 0]) - noise)

gbdt_no_cst = HistGradientBoostingRegressor().fit(X, y)
gbdt_cst = HistGradientBoostingRegressor(monotonic_cst=[1, 0]).fit(X, y)

disp = plot_partial_dependence(
    gbdt_no_cst, X, features=[0], feature_names=['feature 0'],
    line_kw={'linewidth': 4, 'label': 'unconstrained'})
plot_partial_dependence(gbdt_cst, X, features=[0],
    line_kw={'linewidth': 4, 'label': 'constrained'}, ax=disp.axes_)
disp.axes_[0, 0].plot(X[:, 0], y, 'o', alpha=.5, zorder=-1, label='samples')
disp.axes_[0, 0].set_ylim(-3, 3); disp.axes_[0, 0].set_xlim(-1, 1)
plt.legend()
plt.show()

##############################################################################
# Sample-weight support for Lasso and ElasticNet
# ----------------------------------------------
# The two linear regressors :class:`~sklearn.linear_model.Lasso` and
# :class:`~sklearn.linear_model.ElasticNet` now support sample weights.

from sklearn.model_selection import train_test_split
from sklearn.datasets import make_regression
from sklearn.linear_model import Lasso
import numpy as np

n_samples, n_features = 1000, 20
rng = np.random.RandomState(0)
X, y = make_regression(n_samples, n_features, random_state=rng)
sample_weight = rng.rand(n_samples)
X_train, X_test, y_train, y_test, sw_train, sw_test = train_test_split(
    X, y, sample_weight, random_state=rng)
reg = Lasso()
reg.fit(X_train, y_train, sample_weight=sw_train)
print(reg.score(X_test, y_test, sw_test))
