Python: np.where()的使用，注意：它对list列表无效。

x = np.random.randn(4, 4)
print(x)
A = np.where(x>0, 2, -2)
print(A)

结果： 

 

np.where()对列表无效

a = [1,2,2,3,2,5]
print(np.where(a == 2))
print(np.where(a == 2)[0])

结果： 

 

a = np.array(a)
print(np.where(a == 2))
print(np.where(a == 2)[0])