In [1]:

    

import numpy as np


    

In [2]:

    

a = np.arange(9).reshape((3, 3))
print(a)


    

    




[[0 1 2]
 [3 4 5]
 [6 7 8]]

In [3]:

    

print(np.where(a < 4, -1, 100))


    

    




[[ -1  -1  -1]
 [ -1 100 100]
 [100 100 100]]

In [4]:

    

print(np.where(a < 4, True, False))


    

    




[[ True  True  True]
 [ True False False]
 [False False False]]

In [5]:

    

print(a < 4)


    

    




[[ True  True  True]
 [ True False False]
 [False False False]]

In [6]:

    

print(np.where((a > 2) & (a < 6), -1, 100))


    

    




[[100 100 100]
 [ -1  -1  -1]
 [100 100 100]]

In [7]:

    

print(np.where((a > 2) & (a < 6) | (a == 7), -1, 100))


    

    




[[100 100 100]
 [ -1  -1  -1]
 [100  -1 100]]

In [8]:

    

print((a > 2) & (a < 6))


    

    




[[False False False]
 [ True  True  True]
 [False False False]]

In [9]:

    

print((a > 2) & (a < 6) | (a == 7))


    

    




[[False False False]
 [ True  True  True]
 [False  True False]]

In [10]:

    

print(np.where(a < 4, -1, a))


    

    




[[-1 -1 -1]
 [-1  4  5]
 [ 6  7  8]]

In [11]:

    

print(np.where(a < 4, a, 100))


    

    




[[  0   1   2]
 [  3 100 100]
 [100 100 100]]

In [12]:

    

a_org = np.arange(9).reshape((3, 3))
print(a_org)


    

    




[[0 1 2]
 [3 4 5]
 [6 7 8]]

In [13]:

    

a_new = np.where(a_org < 4, -1, a_org)
print(a_new)


    

    




[[-1 -1 -1]
 [-1  4  5]
 [ 6  7  8]]

In [14]:

    

print(a_org)


    

    




[[0 1 2]
 [3 4 5]
 [6 7 8]]

In [15]:

    

a_org[a_org < 4] = -1
print(a_org)


    

    




[[-1 -1 -1]
 [-1  4  5]
 [ 6  7  8]]

In [16]:

    

print(np.where(a < 4, a * 10, a))


    

    




[[ 0 10 20]
 [30  4  5]
 [ 6  7  8]]

In [17]:

    

print(np.where(a < 4))


    

    




(array([0, 0, 0, 1]), array([0, 1, 2, 0]))

In [18]:

    

print(type(np.where(a < 4)))


    

    




<class 'tuple'>

In [19]:

    

print(list(zip(*np.where(a < 4))))


    

    




[(0, 0), (0, 1), (0, 2), (1, 0)]

In [20]:

    

a_3d = np.arange(24).reshape(2, 3, 4)
print(a_3d)


    

    




[[[ 0  1  2  3]
  [ 4  5  6  7]
  [ 8  9 10 11]]

 [[12 13 14 15]
  [16 17 18 19]
  [20 21 22 23]]]

In [21]:

    

print(np.where(a_3d < 5))


    

    




(array([0, 0, 0, 0, 0]), array([0, 0, 0, 0, 1]), array([0, 1, 2, 3, 0]))

In [22]:

    

print(list(zip(*np.where(a_3d < 5))))


    

    




[(0, 0, 0), (0, 0, 1), (0, 0, 2), (0, 0, 3), (0, 1, 0)]

In [23]:

    

a_1d = np.arange(6)
print(a_1d)


    

    




[0 1 2 3 4 5]

In [24]:

    

print(np.where(a_1d < 3))


    

    




(array([0, 1, 2]),)

In [25]:

    

print(list(zip(*np.where(a_1d < 3))))


    

    




[(0,), (1,), (2,)]

In [26]:

    

print(np.where(a_1d < 3)[0])


    

    




[0 1 2]

In [27]:

    

print(np.where(a_1d < 3)[0].tolist())


    

    




[0, 1, 2]