# Source code for yellowbrick.model_selection.learning_curve

```
# yellowbrick.model_selection.learning_curve
# Implements a learning curve visualization for model selection.
#
# Author: Jason Keung <[email protected]>
# Created: Mon May 22 09:22:00 2017 -0500
#
# ID: learning_curve.py [] [email protected] $
"""
Implements a learning curve visualization for model selection.
"""
##########################################################################
## Imports
##########################################################################
import numpy as np
from yellowbrick.base import ModelVisualizer
from yellowbrick.style import resolve_colors
from yellowbrick.exceptions import YellowbrickValueError
from sklearn.model_selection import learning_curve as sk_learning_curve
# Default ticks for the learning curve train sizes
DEFAULT_TRAIN_SIZES = np.linspace(0.1, 1.0, 5)
##########################################################################
## LearningCurve Visualizer
##########################################################################
[docs]class LearningCurve(ModelVisualizer):
"""
Visualizes the learning curve for both test and training data for
different training set sizes. These curves can act as a proxy to
demonstrate the implied learning rate with experience (e.g. how much data
is required to make an adequate model). They also demonstrate if the model
is more sensitive to error due to bias vs. error due to variance and can
be used to quickly check if a model is overfitting.
The visualizer evaluates cross-validated training and test scores for
different training set sizes. These curves are plotted so that the x-axis
is the training set size and the y-axis is the score.
The cross-validation generator splits the whole dataset k times, scores
are averaged over all k runs for the training subset. The curve plots the
mean score for the k splits, and the filled in area suggests the
variability of the cross-validation by plotting one standard deviation
above and below the mean for each split.
Parameters
----------
model : a scikit-learn estimator
An object that implements ``fit`` and ``predict``, can be a
classifier, regressor, or clusterer so long as there is also a valid
associated scoring metric.
Note that the object is cloned for each validation.
ax : matplotlib.Axes object, optional
The axes object to plot the figure on.
groups : array-like, with shape (n_samples,)
Optional group labels for the samples used while splitting the dataset
into train/test sets.
train_sizes : array-like, shape (n_ticks,)
default: ``np.linspace(0.1,1.0,5)``
Relative or absolute numbers of training examples that will be used to
generate the learning curve. If the dtype is float, it is regarded as
a fraction of the maximum size of the training set, otherwise it is
interpreted as absolute sizes of the training sets.
cv : int, cross-validation generator or an iterable, optional
Determines the cross-validation splitting strategy.
Possible inputs for cv are:
- None, to use the default 3-fold cross-validation,
- integer, to specify the number of folds.
- An object to be used as a cross-validation generator.
- An iterable yielding train/test splits.
see the scikit-learn
`cross-validation guide <http://scikit-learn.org/stable/modules/cross_validation.html>`_
for more information on the possible strategies that can be used here.
scoring : string, callable or None, optional, default: None
A string or scorer callable object / function with signature
``scorer(estimator, X, y)``. See scikit-learn model evaluation
documentation for names of possible metrics.
exploit_incremental_learning : boolean, default: False
If the estimator supports incremental learning, this will be used to
speed up fitting for different training set sizes.
n_jobs : integer, optional
Number of jobs to run in parallel (default 1).
pre_dispatch : integer or string, optional
Number of predispatched jobs for parallel execution (default is
all). The option can reduce the allocated memory. The string can
be an expression like '2*n_jobs'.
shuffle : boolean, optional
Whether to shuffle training data before taking prefixes of it
based on``train_sizes``.
random_state : int, RandomState instance or None, optional (default=None)
If int, random_state is the seed used by the random number generator;
If RandomState instance, random_state is the random number generator;
If None, the random number generator is the RandomState instance used
by `np.random`. Used when ``shuffle`` is True.
kwargs : dict
Keyword arguments that are passed to the base class and may influence
the visualization as defined in other Visualizers.
Attributes
----------
train_sizes_ : array, shape = (n_unique_ticks,), dtype int
Numbers of training examples that has been used to generate the
learning curve. Note that the number of ticks might be less
than n_ticks because duplicate entries will be removed.
train_scores_ : array, shape (n_ticks, n_cv_folds)
Scores on training sets.
train_scores_mean_ : array, shape (n_ticks,)
Mean training data scores for each training split
train_scores_std_ : array, shape (n_ticks,)
Standard deviation of training data scores for each training split
test_scores_ : array, shape (n_ticks, n_cv_folds)
Scores on test set.
test_scores_mean_ : array, shape (n_ticks,)
Mean test data scores for each test split
test_scores_std_ : array, shape (n_ticks,)
Standard deviation of test data scores for each test split
Examples
--------
>>> from yellowbrick.model_selection import LearningCurve
>>> from sklearn.naive_bayes import GaussianNB
>>> model = LearningCurve(GaussianNB())
>>> model.fit(X, y)
>>> model.poof()
Notes
-----
This visualizer is essentially a wrapper for the
``sklearn.model_selection.learning_curve utility``, discussed in the
`validation curves <http://scikit-learn.org/stable/modules/learning_curve.html#learning-curve>`_
documentation.
.. seealso:: The documentation for the
`learning_curve <http://scikit-learn.org/stable/modules/generated/sklearn.model_selection.learning_curve.html#sklearn.model_selection.learning_curve>`_
function, which this visualizer wraps.
"""
def __init__(self, model, ax=None, groups=None,
train_sizes=DEFAULT_TRAIN_SIZES, cv=None, scoring=None,
exploit_incremental_learning=False, n_jobs=1,
pre_dispatch="all", shuffle=False, random_state=None,
**kwargs):
# Initialize the model visualizer
super(LearningCurve, self).__init__(model, ax=ax, **kwargs)
# Validate the train sizes
train_sizes = np.asarray(train_sizes)
if train_sizes.ndim != 1:
raise YellowbrickValueError(
"must specify array of train sizes, '{}' is not valid".format(
repr(train_sizes)
))
# Set the metric parameters to be used later
self.set_params(
groups=groups, train_sizes=train_sizes, cv=cv, scoring=scoring,
exploit_incremental_learning=exploit_incremental_learning,
n_jobs=n_jobs, pre_dispatch=pre_dispatch, shuffle=shuffle,
random_state=random_state,
)
[docs] def fit(self, X, y=None):
"""
Fits the learning curve with the wrapped model to the specified data.
Draws training and test score curves and saves the scores to the
estimator.
Parameters
----------
X : array-like, shape (n_samples, n_features)
Training vector, where n_samples is the number of samples and
n_features is the number of features.
y : array-like, shape (n_samples) or (n_samples, n_features), optional
Target relative to X for classification or regression;
None for unsupervised learning.
Returns
-------
self : instance
Returns the instance of the learning curve visualizer for use in
pipelines and other sequential transformers.
"""
# arguments to pass to sk_learning_curve
sklc_kwargs = {
key: self.get_params()[key]
for key in (
'groups', 'train_sizes', 'cv', 'scoring',
'exploit_incremental_learning', 'n_jobs',
'pre_dispatch', 'shuffle', 'random_state',
)
}
# compute the learning curve and store the scores on the estimator
curve = sk_learning_curve(self.estimator, X, y, **sklc_kwargs)
self.train_sizes_, self.train_scores_, self.test_scores_ = curve
# compute the mean and standard deviation of the training data
self.train_scores_mean_ = np.mean(self.train_scores_, axis=1)
self.train_scores_std_ = np.std(self.train_scores_, axis=1)
# compute the mean and standard deviation of the test data
self.test_scores_mean_ = np.mean(self.test_scores_, axis=1)
self.test_scores_std_ = np.std(self.test_scores_, axis=1)
# draw the curves on the current axes
self.draw()
return self
[docs] def draw(self, **kwargs):
"""
Renders the training and test learning curves.
"""
# Specify the curves to draw and their labels
labels = ("Training Score", "Cross Validation Score")
curves = (
(self.train_scores_mean_, self.train_scores_std_),
(self.test_scores_mean_, self.test_scores_std_),
)
# Get the colors for the train and test curves
colors = resolve_colors(n_colors=2)
# Plot the fill betweens first so they are behind the curves.
for idx, (mean, std) in enumerate(curves):
# Plot one standard deviation above and below the mean
self.ax.fill_between(
self.train_sizes_, mean - std, mean+std, alpha=0.25,
color=colors[idx],
)
# Plot the mean curves so they are in front of the variance fill
for idx, (mean, _) in enumerate(curves):
self.ax.plot(
self.train_sizes_, mean, 'o-', color=colors[idx],
label=labels[idx],
)
return self.ax
[docs] def finalize(self, **kwargs):
"""
Add the title, legend, and other visual final touches to the plot.
"""
# Set the title of the figure
self.set_title('Learning Curve for {}'.format(self.name))
# Add the legend
self.ax.legend(frameon=True, loc='best')
# Set the axis labels
self.ax.set_xlabel('Training Instances')
self.ax.set_ylabel('Score')
##########################################################################
## Quick Methods
##########################################################################
def learning_curve(model, X, y, ax=None, groups=None,
train_sizes=DEFAULT_TRAIN_SIZES, cv=None, scoring=None,
exploit_incremental_learning=False, n_jobs=1,
pre_dispatch="all", shuffle=False, random_state=None,
**kwargs):
"""
Displays a learning curve based on number of samples vs training and
cross validation scores. The learning curve aims to show how a model
learns and improves with experience.
This helper function is a quick wrapper to utilize the LearningCurve
for one-off analysis.
Parameters
----------
model : a scikit-learn estimator
An object that implements ``fit`` and ``predict``, can be a
classifier, regressor, or clusterer so long as there is also a valid
associated scoring metric.
Note that the object is cloned for each validation.
X : array-like, shape (n_samples, n_features)
Training vector, where n_samples is the number of samples and
n_features is the number of features.
y : array-like, shape (n_samples) or (n_samples, n_features), optional
Target relative to X for classification or regression;
None for unsupervised learning.
ax : matplotlib.Axes object, optional
The axes object to plot the figure on.
groups : array-like, with shape (n_samples,)
Optional group labels for the samples used while splitting the dataset
into train/test sets.
train_sizes : array-like, shape (n_ticks,)
default: ``np.linspace(0.1,1.0,5)``
Relative or absolute numbers of training examples that will be used to
generate the learning curve. If the dtype is float, it is regarded as
a fraction of the maximum size of the training set, otherwise it is
interpreted as absolute sizes of the training sets.
cv : int, cross-validation generator or an iterable, optional
Determines the cross-validation splitting strategy.
Possible inputs for cv are:
- None, to use the default 3-fold cross-validation,
- integer, to specify the number of folds.
- An object to be used as a cross-validation generator.
- An iterable yielding train/test splits.
see the scikit-learn
`cross-validation guide <http://scikit-learn.org/stable/modules/cross_validation.html>`_
for more information on the possible strategies that can be used here.
scoring : string, callable or None, optional, default: None
A string or scorer callable object / function with signature
``scorer(estimator, X, y)``. See scikit-learn model evaluation
documentation for names of possible metrics.
exploit_incremental_learning : boolean, default: False
If the estimator supports incremental learning, this will be used to
speed up fitting for different training set sizes.
n_jobs : integer, optional
Number of jobs to run in parallel (default 1).
pre_dispatch : integer or string, optional
Number of predispatched jobs for parallel execution (default is
all). The option can reduce the allocated memory. The string can
be an expression like '2*n_jobs'.
shuffle : boolean, optional
Whether to shuffle training data before taking prefixes of it
based on``train_sizes``.
random_state : int, RandomState instance or None, optional (default=None)
If int, random_state is the seed used by the random number generator;
If RandomState instance, random_state is the random number generator;
If None, the random number generator is the RandomState instance used
by `np.random`. Used when ``shuffle`` is True.
kwargs : dict
Keyword arguments that are passed to the base class and may influence
the visualization as defined in other Visualizers. These arguments are
also passed to the `poof()` method, e.g. can pass a path to save the
figure to.
Returns
-------
ax : matplotlib axes
Returns the axes that the learning curve were drawn on.
"""
# Initialize the visualizer
oz = LearningCurve(
model, ax=ax, groups=groups, train_sizes=train_sizes, cv=cv,
scoring=scoring, n_jobs=n_jobs, pre_dispatch=pre_dispatch,
shuffle=shuffle, random_state=random_state,
exploit_incremental_learning=exploit_incremental_learning,
)
# Fit and poof the visualizer
oz.fit(X, y)
oz.poof(**kwargs)
return oz.ax
```