'''
模型效果指标评估
y_true：真实的数据值
y_pred：回归模型预测的数据值
explained_variance_score：解释回归模型的方差得分，其值取值范围是[0,1]，越接近于1说明自变量越能解释因变量
的方差变化，值越小则说明效果越差。
mean_absolute_error：平均绝对误差（Mean Absolute Error，MAE），用于评估预测结果和真实数据集的接近程度的程度
，其其值越小说明拟合效果越好。
mean_squared_error：均方差（Mean squared error，MSE），该指标计算的是拟合数据和原始数据对应样本点的误差的
平方和的均值，其值越小说明拟合效果越好。
r2_score：判定系数，其含义是也是解释回归模型的方差得分，其值取值范围是[0,1]，越接近于1说明自变量越能解释因
变量的方差变化，值越小则说明效果越差。
explained_variance_score解释方差的得分
Parameters:
y_true : array-like of shape = (n_samples) or (n_samples, n_outputs)
Ground truth (correct) target values.
y_pred : array-like of shape = (n_samples) or (n_samples, n_outputs)
Estimated target values.
sample_weight : array-like of shape = (n_samples), optional
Sample weights.
multioutput : string in [‘raw_values’, ‘uniform_average’, ‘variance_weighted’] or array-like of shape (n_outputs)
Defines aggregating of multiple output scores. Array-like value defines weights used to average scores.
‘raw_values’ :
Returns a full set of scores in case of multioutput input.
‘uniform_average’ :
Scores of all outputs are averaged with uniform weight.
‘variance_weighted’ :
Scores of all outputs are averaged, weighted by the variances of each individual output.
Returns:
score : float or ndarray of floats
The explained variance or ndarray if ‘multioutput’ is ‘raw_values’.
>>> from sklearn.metrics import explained_variance_score
>>> y_true = [3, -0.5, 2, 7]
>>> y_pred = [2.5, 0.0, 2, 8]
>>> explained_variance_score(y_true, y_pred)
0.957...
>>> y_true = [[0.5, 1], [-1, 1], [7, -6]]
>>> y_pred = [[0, 2], [-1, 2], [8, -5]]
>>> explained_variance_score(y_true, y_pred, multioutput='uniform_average')
...
0.983...
mean_absolute_error平均绝对误差
sklearn.metrics.mean_absolute_error(y_true, y_pred, sample_weight=None, multioutput=’uniform_average’)
Parameters:
y_true : array-like of shape = (n_samples) or (n_samples, n_outputs)
Ground truth (correct) target values.
y_pred : array-like of shape = (n_samples) or (n_samples, n_outputs)
Estimated target values.
sample_weight : array-like of shape = (n_samples), optional
Sample weights.
multioutput : string in [‘raw_values’, ‘uniform_average’]
or array-like of shape (n_outputs) Defines aggregating of multiple output values. Array-like value defines weights used to average errors.
‘raw_values’ :
Returns a full set of errors in case of multioutput input.
‘uniform_average’ :
Errors of all outputs are averaged with uniform weight.
Returns:
loss : float or ndarray of floats
If multioutput is ‘raw_values’, then mean absolute error is returned for each output separately. If multioutput is ‘uniform_average’ or an ndarray of weights, then the weighted average of all output errors is returned.
MAE output is non-negative floating point. The best value is 0.0.
Examples
>>> from sklearn.metrics import mean_absolute_error
>>> y_true = [3, -0.5, 2, 7]
>>> y_pred = [2.5, 0.0, 2, 8]
>>> mean_absolute_error(y_true, y_pred)
0.5
>>> y_true = [[0.5, 1], [-1, 1], [7, -6]]
>>> y_pred = [[0, 2], [-1, 2], [8, -5]]
>>> mean_absolute_error(y_true, y_pred)
0.75
>>> mean_absolute_error(y_true, y_pred, multioutput='raw_values')
array([0.5, 1. ])
>>> mean_absolute_error(y_true, y_pred, multioutput=[0.3, 0.7])
...
0.85...
mean_squared_error 均方误差
sklearn.metrics.mean_squared_error(y_true, y_pred, sample_weight=None, multioutput=’uniform_average’)
Parameters:
y_true : array-like of shape = (n_samples) or (n_samples, n_outputs)
Ground truth (correct) target values.
y_pred : array-like of shape = (n_samples) or (n_samples, n_outputs)
Estimated target values.
sample_weight : array-like of shape = (n_samples), optional
Sample weights.
multioutput : string in [‘raw_values’, ‘uniform_average’]
or array-like of shape (n_outputs) Defines aggregating of multiple output values. Array-like value defines weights used to average errors.
‘raw_values’ :
Returns a full set of errors in case of multioutput input.
‘uniform_average’ :
Errors of all outputs are averaged with uniform weight.
Returns:
loss : float or ndarray of floats
A non-negative floating point value (the best value is 0.0), or an array of floating point values, one for each individual target.
Examples：
>>> from sklearn.metrics import mean_squared_error
>>> y_true = [3, -0.5, 2, 7]
>>> y_pred = [2.5, 0.0, 2, 8]
>>> mean_squared_error(y_true, y_pred)
0.375
>>> y_true = [[0.5, 1],[-1, 1],[7, -6]]
>>> y_pred = [[0, 2],[-1, 2],[8, -5]]
>>> mean_squared_error(y_true, y_pred)
0.708...
>>> mean_squared_error(y_true, y_pred, multioutput='raw_values')
...
array([0.41666667, 1. ])
>>> mean_squared_error(y_true, y_pred, multioutput=[0.3, 0.7])
...
0.825...
r2_score
sklearn.metrics.r2_score(y_true, y_pred, sample_weight=None, multioutput=’uniform_average’)
Parameters:
y_true : array-like of shape = (n_samples) or (n_samples, n_outputs)
Ground truth (correct) target values.
y_pred : array-like of shape = (n_samples) or (n_samples, n_outputs)
Estimated target values.
sample_weight : array-like of shape = (n_samples), optional
Sample weights.
multioutput : string in [‘raw_values’, ‘uniform_average’, ‘variance_weighted’] or None or array-like of shape (n_outputs)
Defines aggregating of multiple output scores. Array-like value defines weights used to average scores. Default is “uniform_average”.
‘raw_values’ :
Returns a full set of scores in case of multioutput input.
‘uniform_average’ :
Scores of all outputs are averaged with uniform weight.
‘variance_weighted’ :
Scores of all outputs are averaged, weighted by the variances of each individual output.
Changed in version 0.19: Default value of multioutput is ‘uniform_average’.
Returns:
z : float or ndarray of floats
The R^2 score or ndarray of scores if ‘multioutput’ is ‘raw_values’.
Examples
>>> from sklearn.metrics import r2_score
>>> y_true = [3, -0.5, 2, 7]
>>> y_pred = [2.5, 0.0, 2, 8]
>>> r2_score(y_true, y_pred)
0.948...
>>> y_true = [[0.5, 1], [-1, 1], [7, -6]]
>>> y_pred = [[0, 2], [-1, 2], [8, -5]]
>>> r2_score(y_true, y_pred,
... multioutput='variance_weighted')
0.938...
>>> y_true = [1, 2, 3]
>>> y_pred = [1, 2, 3]
>>> r2_score(y_true, y_pred)
1.0
>>> y_true = [1, 2, 3]
>>> y_pred = [2, 2, 2]
>>> r2_score(y_true, y_pred)
0.0
>>> y_true = [1, 2, 3]
>>> y_pred = [3, 2, 1]
>>> r2_score(y_true, y_pred)
-3.0
Median absolute error绝对中位差
sklearn.metrics.median_absolute_error(y_true, y_pred)
Parameters:
y_true : array-like of shape = (n_samples)
Ground truth (correct) target values.
y_pred : array-like of shape = (n_samples)
Estimated target values.
Returns:
loss : float
A positive floating point value (the best value is 0.0).
>>> from sklearn.metrics import median_absolute_error
>>> y_true = [3, -0.5, 2, 7]
>>> y_pred = [2.5, 0.0, 2, 8]
>>> median_absolute_error(y_true, y_pred)
0.5
来源：https://blog.csdn.net/HHG20171226/article/details/102727204