Python sklearn：如何获得多项式特征的系数
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sklearn: how to get coefficients of polynomial features
提问by Moritz
I know it is possible to obtain the polynomial features as numbers by using: polynomial_features.transform(X). According to the manual, for a degree of two the features are: [1, a, b, a^2, ab, b^2]. But how do I obtain a description of the features for higher orders ? .get_params()does not show any list of features.
我知道这是可能通过使用获得多项式特征号：polynomial_features.transform(X)。根据手册，对于两个程度的特征是：[1, a, b, a^2, ab, b^2]。但是我如何获得高阶特征的描述？.get_params()不显示任何功能列表。
采纳答案by prez
By the way, there is more appropriate function now: PolynomialFeatures.get_feature_names.
顺便说一句，现在有更合适的函数： PolynomialFeatures.get_feature_names。
from sklearn.preprocessing import PolynomialFeatures
import pandas as pd
import numpy as np
data = pd.DataFrame.from_dict({
'x': np.random.randint(low=1, high=10, size=5),
'y': np.random.randint(low=-1, high=1, size=5),
})
p = PolynomialFeatures(degree=2).fit(data)
print p.get_feature_names(data.columns)
This will output as follows:
这将输出如下：
['1', 'x', 'y', 'x^2', 'x y', 'y^2']
N.B. For some reason you gotta fit your PolynomialFeatures object before you will be able to use get_feature_names().
注意，出于某种原因，您必须先拟合 PolynomialFeatures 对象，然后才能使用 get_feature_names()。
If you are Pandas-lover (as I am), you can easily form DataFrame with all new features like this:
如果您是 Pandas 爱好者（就像我一样），您可以轻松地使用所有新功能形成 DataFrame，如下所示：
features = DataFrame(p.transform(data), columns=p.get_feature_names(data.columns))
print features
Result will look like this:
结果将如下所示：
1 x y x^2 x y y^2
0 1.0 8.0 -1.0 64.0 -8.0 1.0
1 1.0 9.0 -1.0 81.0 -9.0 1.0
2 1.0 1.0 0.0 1.0 0.0 0.0
3 1.0 6.0 0.0 36.0 0.0 0.0
4 1.0 5.0 -1.0 25.0 -5.0 1.0
回答by omerbp
import numpy as np
from sklearn.preprocessing import PolynomialFeatures
X = np.array([2,3])
poly = PolynomialFeatures(3)
Y = poly.fit_transform(X)
print Y
# prints [[ 1 2 3 4 6 9 8 12 18 27]]
print poly.powers_
This code will print:
此代码将打印：
[[0 0]
[1 0]
[0 1]
[2 0]
[1 1]
[0 2]
[3 0]
[2 1]
[1 2]
[0 3]]
So if the i'th cell is (x,y), that means that Y[i]=(a**x)*(b**y).
For instance, in the code example [2 1]equals to (2**2)*(3**1)=12.
所以如果第 i 个单元格是(x,y)，那就意味着Y[i]=(a**x)*(b**y). 例如，在代码示例中[2 1]等于(2**2)*(3**1)=12。
