82 lines
1.8 KiB
Python
82 lines
1.8 KiB
Python
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# Sebastian Raschka 2014-2020
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# mlxtend Machine Learning Library Extensions
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#
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# Functions for different counting operations.
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# Author: Sebastian Raschka <sebastianraschka.com>
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#
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# License: BSD 3 clause
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def factorial(n):
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if n == 0:
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return 1
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else:
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return n * factorial(n-1)
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def num_combinations(n, k, with_replacement=False):
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"""
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Function to calculate the number of possible combinations.
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Parameters
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----------
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n : `int`
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Total number of items.
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k : `int`
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Number of elements of the target itemset.
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with_replacement : `bool` (default: False)
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Allows repeated elements if True.
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Returns
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----------
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comb : `int`
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Number of possible combinations.
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Examples
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-----------
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For usage examples, please see
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http://rasbt.github.io/mlxtend/user_guide/math/num_combinations/
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"""
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if with_replacement:
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numerator = factorial(n + k - 1)
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denominator = factorial(k) * factorial(n-1)
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else:
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numerator = factorial(n)
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denominator = factorial(k) * factorial(n-k)
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comb = numerator//denominator
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return comb
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def num_permutations(n, k, with_replacement=False):
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"""
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Function to calculate the number of possible permutations.
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Parameters
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----------
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n : `int`
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Total number of items.
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k : `int`
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Number of elements of the target itemset.
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with_replacement : `bool`
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Allows repeated elements if True.
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Returns
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----------
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permut : `int`
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Number of possible permutations.
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Examples
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-----------
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For usage examples, please see
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http://rasbt.github.io/mlxtend/user_guide/math/num_permutations/
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"""
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if with_replacement:
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permut = n**k
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else:
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numerator = factorial(n)
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denominator = factorial(n-k)
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permut = numerator//denominator
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return permut
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