[英]Counting occurrences of columns in numpy array
Given a 2 xd dimensional numpy array M, I want to count the number of occurences of each column of M. That is, I'm looking for a general version of bincount
. 给定一个2 xd维numpy数组M,我想计算M每列的出现次数。也就是说,我正在寻找bincount
的一般版本。
What I tried so far: (1) Converted columns to tuples (2) Hashed tuples (via hash
) to natural numbers (3) used numpy.bincount
. 到目前为止我尝试过:(1)将列转换为元组(2)使用numpy.bincount
将哈希元组(通过hash
)转换为自然数(3)。
This seems rather clumsy. 这看起来很笨拙。 Is anybody aware of a more elegant and efficient way? 有人知道更优雅高效的方式吗?
You can use collections.Counter
: 你可以使用collections.Counter
:
>>> import numpy as np
>>> a = np.array([[ 0, 1, 2, 4, 5, 1, 2, 3],
... [ 4, 5, 6, 8, 9, 5, 6, 7],
... [ 8, 9, 10, 12, 13, 9, 10, 11]])
>>> from collections import Counter
>>> Counter(map(tuple, a.T))
Counter({(2, 6, 10): 2, (1, 5, 9): 2, (4, 8, 12): 1, (5, 9, 13): 1, (3, 7, 11):
1, (0, 4, 8): 1})
Given: 鉴于:
a = np.array([[ 0, 1, 2, 4, 5, 1, 2, 3],
[ 4, 5, 6, 8, 9, 5, 6, 7],
[ 8, 9, 10, 12, 13, 9, 10, 11]])
b = np.transpose(a)
A more efficient solution than hashing (still requires manipulation): 比散列更有效的解决方案(仍需要操作):
I create a view of the array with the flexible data type np.void
(see here ) such that each row becomes a single element. 我使用灵活的数据类型np.void
(参见此处 )创建数组视图,使每行成为单个元素。 Converting to this shape will allow np.unique
to operate on it. 转换为此形状将允许np.unique
进行操作。
%%timeit c = np.ascontiguousarray(b).view(np.dtype((np.void, b.dtype.itemsize*b.shape[1]))) _, index, counts = np.unique(c, return_index = True, return_counts = True) #counts are in the last column, remember original array is transposed >>>np.concatenate((b[idx], cnt[:, None]), axis = 1) array([[ 0, 4, 8, 1], [ 1, 5, 9, 2], [ 2, 6, 10, 2], [ 3, 7, 11, 1], [ 4, 8, 12, 1], [ 5, 9, 13, 1]]) 10000 loops, best of 3: 65.4 µs per loop
The counts appended to the unique columns of a
. 计数追加到的唯一列a
。
Your hashing solution. 您的哈希解决方案。
%%timeit array_hash = [hash(tuple(row)) for row in b] uniq, index, counts = np.unique(array_hash, return_index= True, return_counts = True) np.concatenate((b[idx], cnt[:, None]), axis = 1) 10000 loops, best of 3: 89.5 µs per loop
Update : Eph's solution is the most efficient and elegant. 更新 :Eph的解决方案是最有效和最优雅的。
%%timeit
Counter(map(tuple, a.T))
10000 loops, best of 3: 38.3 µs per loop
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