NumPy - 2

import numpy as np

## Copy Vs View

arr = np.array([1,2,3,4,5])
myarray = arr.copy()
# myarray[0] = 42
arr[0] = 10
print('arr:', arr)
print('myarray:', myarray)

arr: [10  2  3  4  5]
myarray: [1 2 3 4 5]

arr = np.array([1,2,3,4,5])
myarray = arr.view()
myarray[0] = 40
arr[0] = 10
print('arr:', arr)
print('myarray:', myarray)

arr: [10  2  3  4  5]
myarray: [10  2  3  4  5]

print(myarray.base)

[10  2  3  4  5]

print(arr.base)

None

arr = np.array([1,2,3,4,5])
myarray = arr.copy()
print(myarray.base)

None

## Shape

arr = np.array(10)
print(arr.shape)

()

arr1 = np.array([1,2,3,4,5])
print(arr1.shape)

(5,)

arr2 = np.array([[1,2],[3,5]])
print(arr2.shape)

(2, 2)

arr3 = np.array([[[1,2,3],[4,5,6]], [[1,2,3],[4,5,6]]])
print(arr3.shape)

(2, 2, 3)

arrn = np.array([1,2,3], ndmin=5)
print(arrn)
print(arrn.shape)

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

## reshape

arr = np.array([[[1,2],[4,5]], [[1,2],[4,5]]])
print(arr)

[[[1 2]
  [4 5]]

 [[1 2]
  [4 5]]]

arr.reshape(2,4)

array([[1, 2, 4, 5],
       [1, 2, 4, 5]])

arr.reshape(3,4)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-65-6e762b0d3244> in <module>
----> 1 arr.reshape(3,4)

ValueError: cannot reshape array of size 8 into shape (3,4)

myarray = arr.reshape(8)
print(myarray)

[1 2 4 5 1 2 4 5]

print(myarray.base)

[[[1 2]
  [4 5]]

 [[1 2]
  [4 5]]]

arr.reshape(2,2,2)

array([[[1, 2],
        [4, 5]],

       [[1, 2],
        [4, 5]]])

arr.reshape(2,-1)

array([[1, 2, 4, 5],
       [1, 2, 4, 5]])

arr.reshape(-1,2,2)  ### (x * 2 * 2 = 8 =>  x = 2)

array([[[1, 2],
        [4, 5]],

       [[1, 2],
        [4, 5]]])

arr.reshape(-1)

array([1, 2, 4, 5, 1, 2, 4, 5])

## iterating arrays

myarray = np.array([1,2,3])
myarray2 = np.array([[1,2,3],[4,5,6]])
myarray3 = np.array([[[1,2,3],[4,5,6]],[[1,2,3],[4,5,6]]])

for x in myarray:
    print(x)

1
2
3

for x in myarray2:
    print(x)

[1 2 3]
[4 5 6]

for x in myarray2:
    for y in x:
        print(y)

1
2
3
4
5
6

for x in myarray3:
    for y in x:
        print(y)

[1 2 3]
[4 5 6]
[1 2 3]
[4 5 6]

for x in myarray3:
    for y in x:
        for z in y:
            print(z)

1
2
3
4
5
6
1
2
3
4
5
6

for x in np.nditer(myarray3):
    print(x)

1
2
3
4
5
6
1
2
3
4
5
6

print(myarray2)

[[1 2 3]
 [4 5 6]]

for x in np.nditer(myarray2[ 1: , ::2]):
    print(x)

4
6

for idx, x in np.ndenumerate(myarray2):
    print(idx, x)

(0, 0) 1
(0, 1) 2
(0, 2) 3
(1, 0) 4
(1, 1) 5
(1, 2) 6

for idx, x in np.ndenumerate(myarray):
    print(idx, x)

(0,) 1
(1,) 2
(2,) 3

print(myarray3)

[[[1 2 3]
  [4 5 6]]

 [[1 2 3]
  [4 5 6]]]

for x in np.nditer(myarray3[:1,1:,::2]):
    print(x)

4
6

for idx, x in np.ndenumerate(myarray3):
    print(idx, x)

(0, 0, 0) 1
(0, 0, 1) 2
(0, 0, 2) 3
(0, 1, 0) 4
(0, 1, 1) 5
(0, 1, 2) 6
(1, 0, 0) 1
(1, 0, 1) 2
(1, 0, 2) 3
(1, 1, 0) 4
(1, 1, 1) 5
(1, 1, 2) 6