ndarrayにおける色んな参照方法をやってみた

import numpy as np
print(np.__version__)
data = np.array([[1,2,3,4,5], [10,20,30,40,50], [100,200,300,400,500]])
print(data)

1.19.2
[[  1   2   3   4   5]
 [ 10  20  30  40  50]
 [100 200 300 400 500]]

取得

d = data[1]
print(d)

[10 20 30 40 50]

d = data[[1]]
print(d)

[[10 20 30 40 50]]

d = data[:,2]
print(d)

[  3  30 300]

d = data[:,2:3]
print(d)

[[  3]
 [ 30]
 [300]]

d = data[1,2:4]
print(d)

[30 40]

d = data[1:2,2:4]
print(d)

[[30 40]]

d = data[1,2]
print(d)

d = data[1,2:3]
print(d)

[30]

d = data[1:2,2:3]
print(d)

[[30]]

d = data[[0,1,2],1]
print(d)

[  2  20 200]

d = data[1,[1,2,3]]
print(d)

[20 30 40]

d = data[[1,2],[2,4]]
print(d)

[ 30 500]

d = data[[0,1],[1,2,3]]
print(d)

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-14-d9878e643f58> in <module>
----> 1 d = data[[0,1],[1,2,3]]
      2 print(d)

IndexError: shape mismatch: indexing arrays could not be broadcast together with shapes (2,) (3,)

d = data[np.ix_([0, 1], [1,2,3])]
print(d)

[[ 2  3  4]
 [20 30 40]]

代入

data1 = data.copy()
data1[1] = 1000
print(data1)

[[   1    2    3    4    5]
 [1000 1000 1000 1000 1000]
 [ 100  200  300  400  500]]

data1 = data.copy()
data1[[1]] = 1000
print(data1)

[[   1    2    3    4    5]
 [1000 1000 1000 1000 1000]
 [ 100  200  300  400  500]]

data1 = data.copy()
data1[:,2] = 1000
print(data1)

[[   1    2 1000    4    5]
 [  10   20 1000   40   50]
 [ 100  200 1000  400  500]]

data1 = data.copy()
data1[:,2:3] = 1000
print(data1)

[[   1    2 1000    4    5]
 [  10   20 1000   40   50]
 [ 100  200 1000  400  500]]

data1 = data.copy()
data1[1,2:4] = 1000
print(data1)

[[   1    2    3    4    5]
 [  10   20 1000 1000   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
data1[1:2,2:4] = 1000
print(data1)

[[   1    2    3    4    5]
 [  10   20 1000 1000   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
data1[1,2] = 1000
print(data1)

[[   1    2    3    4    5]
 [  10   20 1000   40   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
data1[1,2:3] = 1000
print(data1)

[[   1    2    3    4    5]
 [  10   20 1000   40   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
data1[1:2,2:3] = 1000
print(data1)

[[   1    2    3    4    5]
 [  10   20 1000   40   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
data1[[0,1,2],1] = 1000
print(data1)

[[   1 1000    3    4    5]
 [  10 1000   30   40   50]
 [ 100 1000  300  400  500]]

data1 = data.copy()
data1[1,[1,2,3]] = 1000
print(data1)

[[   1    2    3    4    5]
 [  10 1000 1000 1000   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
data1[np.ix_([0, 1], [1,2,3])] = 1000
print(data1)

[[   1 1000 1000 1000    5]
 [  10 1000 1000 1000   50]
 [ 100  200  300  400  500]]

関数呼び出し

def hoge(d):
    print(d)
    d[0] = 2000
    print(d)

data1 = data.copy()
hoge(data1[1])
print(data1)

[10 20 30 40 50]
[2000   20   30   40   50]
[[   1    2    3    4    5]
 [2000   20   30   40   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
hoge(data1[[1]])
print(data1)

[[10 20 30 40 50]]
[[2000 2000 2000 2000 2000]]
[[  1   2   3   4   5]
 [ 10  20  30  40  50]
 [100 200 300 400 500]]

data1 = data.copy()
hoge(data1[:,2])
print(data1)

[  3  30 300]
[2000   30  300]
[[   1    2 2000    4    5]
 [  10   20   30   40   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
hoge(data1[:,2:3])
print(data1)

[[  3]
 [ 30]
 [300]]
[[2000]
 [  30]
 [ 300]]
[[   1    2 2000    4    5]
 [  10   20   30   40   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
hoge(data1[1,2:4])
print(data1)

[30 40]
[2000   40]
[[   1    2    3    4    5]
 [  10   20 2000   40   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
hoge(data1[1:2,2:4])
print(data1)

[[30 40]]
[[2000 2000]]
[[   1    2    3    4    5]
 [  10   20 2000 2000   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
hoge(data1[1,2])
print(data1)

30
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-65-07c98b5a0381> in <module>
      1 data1 = data.copy()
----> 2 hoge(data1[1,2])
      3 print(data1)

<ipython-input-58-7cd04c1a5a75> in hoge(d)
      1 def hoge(d):
      2     print(d)
----> 3     d[0] = 2000
      4     print(d)

TypeError: 'numpy.int32' object does not support item assignment

data1 = data.copy()
hoge(data1[1,2:3])
print(data1)

[30]
[2000]
[[   1    2    3    4    5]
 [  10   20 2000   40   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
hoge(data1[1:2,2:3])
print(data1)

[[30]]
[[2000]]
[[   1    2    3    4    5]
 [  10   20 2000   40   50]
 [ 100  200  300  400  500]]

data1 = data.copy()
hoge(data1[[0,1,2],1])
print(data1)

[  2  20 200]
[2000   20  200]
[[  1   2   3   4   5]
 [ 10  20  30  40  50]
 [100 200 300 400 500]]

data1 = data.copy()
hoge(data1[1,[1,2,3]])
print(data1)

[20 30 40]
[2000   30   40]
[[  1   2   3   4   5]
 [ 10  20  30  40  50]
 [100 200 300 400 500]]

data1 = data.copy()
hoge(data1[np.ix_([0, 1], [1,2,3])])
print(data1)

[[ 2  3  4]
 [20 30 40]]
[[2000 2000 2000]
 [  20   30   40]]
[[  1   2   3   4   5]
 [ 10  20  30  40  50]
 [100 200 300 400 500]]