Python，在 np 中查找数字索引的最快方法。 大批

Question

The fastest way to find numbers indexes in np. array in Python is?

Suppose we have a list of numbers from 0 to 20, and we want to know the indexes of digits 2 and 5

Answer 1

The canonical way would be to use numpy's where method:

a = np.array(range(20))
np.where((a == 2) | (a == 5))

Note that in order to combine the two terms (a == 2) and (a == 5) we need the bitwise or operator | . The reason is that both (a == 2) and (a == 5) return a numpy array of dtype('bool') :

>>> a == 2
array([False, False,  True, False, False, False, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False])

>>> (a == 5)
array([False, False, False, False, False,  True, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False])

>>> (a == 2) | (a==5)
array([False, False,  True, False, False,  True, False, False, False,
       False, False, False, False, False, False, False, False, False,
       False, False])