wehub-resource-sync
58 lines
1.3 KiB
Python
Executable File
58 lines
1.3 KiB
Python
Executable File
import itertools
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import functools
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import numpy as np
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class PolynomialFeature(object):
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"""
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polynomial features
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transforms input array with polynomial features
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Example
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=======
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x =
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[[a, b],
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[c, d]]
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y = PolynomialFeatures(degree=2).transform(x)
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y =
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[[1, a, b, a^2, a * b, b^2],
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[1, c, d, c^2, c * d, d^2]]
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"""
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def __init__(self, degree=2):
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"""
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construct polynomial features
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Parameters
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----------
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degree : int
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degree of polynomial
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"""
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assert isinstance(degree, int)
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self.degree = degree
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def transform(self, x):
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"""
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transforms input array with polynomial features
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Parameters
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----------
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x : (sample_size, n) ndarray
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input array
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Returns
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-------
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output : (sample_size, 1 + nC1 + ... + nCd) ndarray
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polynomial features
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"""
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if x.ndim == 1:
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x = x[:, None]
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x_t = x.transpose()
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features = [np.ones(len(x))]
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for degree in range(1, self.degree + 1):
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for items in itertools.combinations_with_replacement(x_t, degree):
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features.append(functools.reduce(lambda x, y: x * y, items))
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return np.asarray(features).transpose()
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