不同长度的numpy数组的元素比较

Question

I want to compare the elements of two 3D numpy arrays of different lengths. The goal is, to find overlapping elements in the two arrays.

All functions I found so far, rely on the two arrays being of the same lengths.

Is there an efficient way to do compare the 2D-elements (for loops will be very inefficient, since each array has tens of thousands of elements)?

Answer 1

Is intersect1d what you want? For example, if your arrays are a and b , you could simply do:

duplicates = np.intersect1d(a, b)

Answer 2

Here a few ways of comparing 2 1d arrays:

In [325]: n=np.arange(0,10)
In [326]: m=np.arange(3,9)

In [327]: np.in1d(n,m)
Out[327]: array([False, False, False,  True,  True,  True,  True,  True,  True, False], dtype=bool)

In [328]: np.in1d(m,n)
Out[328]: array([ True,  True,  True,  True,  True,  True], dtype=bool)

In [329]: n[:,None]==m[None,:]
Out[329]: 
array([[False, False, False, False, False, False],
       [False, False, False, False, False, False],
       [False, False, False, False, False, False],
       [ True, False, False, False, False, False],
       [False,  True, False, False, False, False],
       [False, False,  True, False, False, False],
       [False, False, False,  True, False, False],
       [False, False, False, False,  True, False],
       [False, False, False, False, False,  True],
       [False, False, False, False, False, False]], dtype=bool)

and farenorth s suggestion

In [330]: np.intersect1d(n,m)
Out[330]: array([3, 4, 5, 6, 7, 8])

In [331]: np.where(np.in1d(n,m))
Out[331]: (array([3, 4, 5, 6, 7, 8], dtype=int64),)