当我尝试从sklearn导入度量时，出现以下错误：
from sklearn.metrics import mean_absolute_percentage_error
ImportError: cannot import name 'mean_absolute_percentage_error' from 'sklearn.metrics'
/Users/carter/opt/anaconda3/lib/python3.8/site-packages/sklearn/metrics/__init__.py)
我已经尝试使用conda update all命令以及重新安装scikit-learn，但问题依旧。还有其他可能的原因和解决方法吗？
mean_absolute_percentage_error 函数是 scikit-learn 版本 0.24 的新功能，如文档中所述。
截至2020年12月，Anaconda 提供的最新版本为 v0.23.2，因此您无法导入 mean_absolute_percentage_error。
上面的答案是正确的。对于那些无法从源代码进行升级/安装的人，下面是所需的代码。
该函数本身依赖于其他函数-一个在同一模块中定义的函数，另外一些来自sklearn.utils.validation。
这是我从源代码中提取的所需代码 - 如果有人需要它（而且我希望我没有违反任何许可证）:
from sklearn.utils.validation import check_consistent_length, check_array
def mean_absolute_percentage_error(y_true, y_pred,
sample_weight=None,
multioutput='uniform_average'):
"""Mean absolute percentage error regression loss.
Note here that we do not represent the output as a percentage in range
[0, 100]. Instead, we represent it in range [0, 1/eps]. Read more in the
:ref:`User Guide <mean_absolute_percentage_error>`.
.. versionadded:: 0.24
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,), default=None
Sample weights.
multioutput : {'raw_values', 'uniform_average'} or array-like
Defines aggregating of multiple output values.
Array-like value defines weights used to average errors.
If input is list then the shape must be (n_outputs,).
'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 in the range [0, 1/eps]
If multioutput is 'raw_values', then mean absolute percentage 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.
MAPE output is non-negative floating point. The best value is 0.0.
But note the fact that bad predictions can lead to arbitarily large
MAPE values, especially if some y_true values are very close to zero.
Note that we return a large value instead of `inf` when y_true is zero.
Examples
--------
>>> from sklearn.metrics import mean_absolute_percentage_error
>>> y_true = [3, -0.5, 2, 7]
>>> y_pred = [2.5, 0.0, 2, 8]
>>> mean_absolute_percentage_error(y_true, y_pred)
0.3273...
>>> y_true = [[0.5, 1], [-1, 1], [7, -6]]
>>> y_pred = [[0, 2], [-1, 2], [8, -5]]
>>> mean_absolute_percentage_error(y_true, y_pred)
0.5515...
>>> mean_absolute_percentage_error(y_true, y_pred, multioutput=[0.3, 0.7])
0.6198...
"""
y_type, y_true, y_pred, multioutput = _check_reg_targets(
y_true, y_pred, multioutput)
check_consistent_length(y_true, y_pred, sample_weight)
epsilon = np.finfo(np.float64).eps
mape = np.abs(y_pred - y_true) / np.maximum(np.abs(y_true), epsilon)
output_errors = np.average(mape,
weights=sample_weight, axis=0)
if isinstance(multioutput, str):
if multioutput == 'raw_values':
return output_errors
elif multioutput == 'uniform_average':
# pass None as weights to np.average: uniform mean
multioutput = None
return np.average(output_errors, weights=multioutput)
def _check_reg_targets(y_true, y_pred, multioutput, dtype="numeric"):
"""Check that y_true and y_pred belong to the same regression task.
Parameters
----------
y_true : array-like
y_pred : array-like
multioutput : array-like or string in ['raw_values', uniform_average',
'variance_weighted'] or None
None is accepted due to backward compatibility of r2_score().
Returns
-------
type_true : one of {'continuous', continuous-multioutput'}
The type of the true target data, as output by
'utils.multiclass.type_of_target'.
y_true : array-like of shape (n_samples, n_outputs)
Ground truth (correct) target values.
y_pred : array-like of shape (n_samples, n_outputs)
Estimated target values.
multioutput : array-like of shape (n_outputs) or string in ['raw_values',
uniform_average', 'variance_weighted'] or None
Custom output weights if ``multioutput`` is array-like or
just the corresponding argument if ``multioutput`` is a
correct keyword.
dtype : str or list, default="numeric"
the dtype argument passed to check_array.
"""
check_consistent_length(y_true, y_pred)
y_true = check_array(y_true, ensure_2d=False, dtype=dtype)
y_pred = check_array(y_pred, ensure_2d=False, dtype=dtype)
if y_true.ndim == 1:
y_true = y_true.reshape((-1, 1))
if y_pred.ndim == 1:
y_pred = y_pred.reshape((-1, 1))
if y_true.shape[1] != y_pred.shape[1]:
raise ValueError("y_true and y_pred have different number of output "
"({0}!={1})".format(y_true.shape[1], y_pred.shape[1]))
n_outputs = y_true.shape[1]
allowed_multioutput_str = ('raw_values', 'uniform_average',
'variance_weighted')
if isinstance(multioutput, str):
if multioutput not in allowed_multioutput_str:
raise ValueError("Allowed 'multioutput' string values are {}. "
"You provided multioutput={!r}".format(
allowed_multioutput_str,
multioutput))
elif multioutput is not None:
multioutput = check_array(multioutput, ensure_2d=False)
if n_outputs == 1:
raise ValueError("Custom weights are useful only in "
"multi-output cases.")
elif n_outputs != len(multioutput):
raise ValueError(("There must be equally many custom weights "
"(%d) as outputs (%d).") %
(len(multioutput), n_outputs))
y_type = 'continuous' if n_outputs == 1 else 'continuous-multioutput'
return y_type, y_true, y_pred, multioutput
!pip install scikit-learn==0.24
那么，
from sklearn.metrics import mean_absolute_percentage_error
def MAPE(y_true, y_pred):
y_true, y_pred = np.array(y_true), np.array(y_pred)
return np.mean(np.abs((y_true - y_pred) / y_true)) * 100
但是上述函数的问题在于当你有（0）真值时，MAPE将变为（inf）。因此，为了解决这个问题，我们使用以下方法：
def MAPE(y_true, y_pred):
y_true, y_pred = np.array(y_true), np.array(y_pred)
return np.mean(np.abs((y_true - y_pred) / np.maximum(np.ones(len(y_true)), np.abs(y_true))))*100
刚遇到了同样的问题。访问正在使用的Anaconda提示符环境，并运行
pip install scikit-learn
问题已解决。
更新了scikit-learn的版本（此时升级到1.0.2版本，但从0.24版本开始就有），现在可以导入和运行sklearn.metrics.mean_absolute_percentage_error。
这里是一个示例（源代码）：
>>> from sklearn.metrics import mean_absolute_percentage_error
>>> y_true = [3, -0.5, 2, 7]
>>> y_pred = [2.5, 0.0, 2, 8]
>>> mean_absolute_percentage_error(y_true, y_pred)
0.3273...
注意：你可能需要记住 MAPE 可能会出现问题，因为它可能导致零除法（ 看看我在这里的回答）。