从一个数组中删除另一个数组中的元素 [英] Removing elements from an array that are in another array
问题描述
说我有这些二维数组A和B.
Say I have these 2D arrays A and B.
如何从A中删除B中的元素(集合论中的补语:A-B)
How can I remove elements from A that are in B. (Complement in set theory: A-B)
A=np.asarray([[1,1,1], [1,1,2], [1,1,3], [1,1,4]])
B=np.asarray([[0,0,0], [1,0,2], [1,0,3], [1,0,4], [1,1,0], [1,1,1], [1,1,4]])
#output = [[1,1,2], [1,1,3]]
更准确地说,我想做这样的事情.
To be more precise, I would like to do something like this.
data = some numpy array
label = some numpy array
A = np.argwhere(label==0) #[[1 1 1], [1 1 2], [1 1 3], [1 1 4]]
B = np.argwhere(data>1.5) #[[0 0 0], [1 0 2], [1 0 3], [1 0 4], [1 1 0], [1 1 1], [1 1 4]]
out = np.argwhere(label==0 and data>1.5) #[[1 1 2], [1 1 3]]
推荐答案
基于 this solution
到 Find the row indexes of several values in a numpy array
,这是一个基于NumPy的解决方案具有较少的内存占用,并且在使用大型阵列时可能会有所帮助-
Based on this solution
to Find the row indexes of several values in a numpy array
, here's a NumPy based solution with less memory footprint and could be beneficial when working with large arrays -
dims = np.maximum(B.max(0),A.max(0))+1
out = A[~np.in1d(np.ravel_multi_index(A.T,dims),np.ravel_multi_index(B.T,dims))]
样品运行-
In [38]: A
Out[38]:
array([[1, 1, 1],
[1, 1, 2],
[1, 1, 3],
[1, 1, 4]])
In [39]: B
Out[39]:
array([[0, 0, 0],
[1, 0, 2],
[1, 0, 3],
[1, 0, 4],
[1, 1, 0],
[1, 1, 1],
[1, 1, 4]])
In [40]: out
Out[40]:
array([[1, 1, 2],
[1, 1, 3]])
对大型阵列的运行时测试-
Runtime test on large arrays -
In [107]: def in1d_approach(A,B):
...: dims = np.maximum(B.max(0),A.max(0))+1
...: return A[~np.in1d(np.ravel_multi_index(A.T,dims),\
...: np.ravel_multi_index(B.T,dims))]
...:
In [108]: # Setup arrays with B as large array and A contains some of B's rows
...: B = np.random.randint(0,9,(1000,3))
...: A = np.random.randint(0,9,(100,3))
...: A_idx = np.random.choice(np.arange(A.shape[0]),size=10,replace=0)
...: B_idx = np.random.choice(np.arange(B.shape[0]),size=10,replace=0)
...: A[A_idx] = B[B_idx]
...:
基于broadcasting
的解决方案的计时-
Timings with broadcasting
based solutions -
In [109]: %timeit A[np.all(np.any((A-B[:, None]), axis=2), axis=0)]
100 loops, best of 3: 4.64 ms per loop # @Kasramvd's soln
In [110]: %timeit A[~((A[:,None,:] == B).all(-1)).any(1)]
100 loops, best of 3: 3.66 ms per loop
基于更少内存占用空间的解决方案-
Timing with less memory footprint based solution -
In [111]: %timeit in1d_approach(A,B)
1000 loops, best of 3: 231 µs per loop
进一步的性能提升
in1d_approach
通过将每一行视为索引元组来减少每一行.通过使用np.dot
引入矩阵乘法,我们可以更有效地完成上述任务,就像-
in1d_approach
reduces each row by considering each row as an indexing tuple. We can do the same a bit more efficiently by introducing matrix-multiplication with np.dot
, like so -
def in1d_dot_approach(A,B):
cumdims = (np.maximum(A.max(),B.max())+1)**np.arange(B.shape[1])
return A[~np.in1d(A.dot(cumdims),B.dot(cumdims))]
让我们在更大的数组上针对以前的版本进行测试-
Let's test it against the previous on much larger arrays -
In [251]: # Setup arrays with B as large array and A contains some of B's rows
...: B = np.random.randint(0,9,(10000,3))
...: A = np.random.randint(0,9,(1000,3))
...: A_idx = np.random.choice(np.arange(A.shape[0]),size=10,replace=0)
...: B_idx = np.random.choice(np.arange(B.shape[0]),size=10,replace=0)
...: A[A_idx] = B[B_idx]
...:
In [252]: %timeit in1d_approach(A,B)
1000 loops, best of 3: 1.28 ms per loop
In [253]: %timeit in1d_dot_approach(A, B)
1000 loops, best of 3: 1.2 ms per loop
这篇关于从一个数组中删除另一个数组中的元素的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!