2.7. Array Slice¶
2.7.1. 1-dimensional Array¶
import numpy as np
a = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9])
a[1:5] # array([2, 3, 4, 5])
a[3:8] # array([4, 5, 6, 7, 8])
a[0:5] # array([1, 2, 3, 4, 5])
a[:5] # array([1, 2, 3, 4, 5])
a[5:9] # array([6, 7, 8, 9])
a[5:len(a)] # array([6, 7, 8, 9])
a[5:] # array([6, 7, 8, 9])
a[-2:] # array([8, 9])
a[-5:] # array([5, 6, 7, 8, 9])
a[-6:-2] # array([4, 5, 6, 7])
a[3:8:2] # array([4, 6, 8])
a[-8:-3:2] # array([2, 4, 6])
a[::2] # array([1, 3, 5, 7, 9])
a[1::2] # array([2, 4, 6, 8])
a[0:len(a)] # array([1, 2, 3, 4, 5, 6, 7, 8, 9])
a[0:] # array([1, 2, 3, 4, 5, 6, 7, 8, 9])
a[:len(a)] # array([1, 2, 3, 4, 5, 6, 7, 8, 9])
a[:] # array([1, 2, 3, 4, 5, 6, 7, 8, 9])
2.7.2. 2-dimensional Array¶
import numpy as np
a = np.array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
a[:]
# array([[1, 2, 3],
# [4, 5, 6],
# [7, 8, 9]])
a[1:]
# array([[4, 5, 6],
# [7, 8, 9]])
a[:1]
# array([[1, 2, 3]])
a[1:3]
# array([[4, 5, 6],
# [7, 8, 9]])
a[::2]
# array([[1, 2, 3],
# [7, 8, 9]])
a[1::2]
# array([[4, 5, 6]])
import numpy as np
a = np.array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
a[:, 0]
# array([1, 4, 7])
a[:, 1]
# array([2, 5, 8])
a[:, 2]
# array([3, 6, 9])
a[:, -1]
# array([3, 6, 9])
a[:, 0:1]
# array([[1],
# [4],
# [7]])
a[:, 0:2]
# array([[1, 2],
# [4, 5],
# [7, 8]])
a[:, :2]
# array([[1, 2],
# [4, 5],
# [7, 8]])
a[:, ::2]
# array([[1, 3],
# [4, 6],
# [7, 9]])
a[:, 1::2]
# array([[2],
# [5],
# [8]])
import numpy as np
a = np.array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
a[0:1, 0:1]
# array([[1]])
a[0:1, 0:2]
# array([[1, 2]])
a[0:1, 0:3]
# array([[1, 2, 3]])
a[0:2, 0:2]
# array([[1, 2],
# [4, 5]])
a[-1:, -2:]
# array([[8, 9]])
a[::2, ::2]
# array([[1, 3],
# [7, 9]])
a[1::2, 1::2]
# array([[5]])
a[[2,1], ::2]
# array([[7, 9],
# [4, 6]])
2.7.3. Assignments¶
2.7.3.1. Numpy Slice 1¶
Assignment: Numpy Slice 1
Last update: 2020-10-01
Complexity: easy
Lines of code: 3 lines
Estimated time: 3 min
Filename:
assignments/numpy_slice_1.py
- English:
Use data from "Given" section (see below)
Print inner 2x2 elements
Compare result with "Tests" section (see below)
- Polish:
Użyj danych z sekcji "Given" (patrz poniżej)
Wybierz wewnętrzne 2x2 elementy
Porównaj wyniki z sekcją "Tests" (patrz poniżej)
- Given:
DATA = np.array([ [2, 8, 1, 5], [8, 8, 4, 4], [5, 5, 2, 5], [1, 0, 6, 0], ])
Tests:
>>> type(result)
np.ndarray
>>> result
array([[8, 4],
[5, 2]])
2.7.3.2. Numpy Slice 2¶
Assignment: Numpy Slice 2
Last update: 2020-10-01
Complexity: easy
Lines of code: 3 lines
Estimated time: 3 min
Filename:
assignments/numpy_slice_2.py
- English:
Use data from "Given" section (see below)
Print inner 4x4 elements
Inner matrix is exactly in the middle of outer
- Polish:
Użyj danych z sekcji "Given" (patrz poniżej)
Wypisz środkowe 4x4 elementy
Środkowa macierz jest dokładnie w środku większej
- Given:
DATA = np.array([[5, 0, 3, 3, 7, 9, 3, 5, 2, 4, 7, 6, 8, 8, 1, 6], [7, 7, 8, 1, 5, 9, 8, 9, 4, 3, 0, 3, 5, 0, 2, 3], [8, 1, 3, 3, 3, 7, 0, 1, 9, 9, 0, 4, 7, 3, 2, 7], [2, 0, 0, 4, 5, 5, 6, 8, 4, 1, 4, 9, 8, 1, 1, 7], [9, 9, 3, 6, 7, 2, 0, 3, 5, 9, 4, 4, 6, 4, 4, 3], [4, 4, 8, 4, 3, 7, 5, 5, 0, 1, 5, 9, 3, 0, 5, 0], [1, 2, 4, 2, 0, 3, 2, 0, 7, 5, 9, 0, 2, 7, 2, 9], [2, 3, 3, 2, 3, 4, 1, 2, 9, 1, 4, 6, 8, 2, 3, 0], [0, 6, 0, 6, 3, 3, 8, 8, 8, 2, 3, 2, 0, 8, 8, 3], [8, 2, 8, 4, 3, 0, 4, 3, 6, 9, 8, 0, 8, 5, 9, 0], [9, 6, 5, 3, 1, 8, 0, 4, 9, 6, 5, 7, 8, 8, 9, 2], [8, 6, 6, 9, 1, 6, 8, 8, 3, 2, 3, 6, 3, 6, 5, 7], [0, 8, 4, 6, 5, 8, 2, 3, 9, 7, 5, 3, 4, 5, 3, 3], [7, 9, 9, 9, 7, 3, 2, 3, 9, 7, 7, 5, 1, 2, 2, 8], [1, 5, 8, 4, 0, 2, 5, 5, 0, 8, 1, 1, 0, 3, 8, 8], [4, 4, 0, 9, 3, 7, 3, 2, 1, 1, 2, 1, 4, 2, 5, 5]])
- Tests:
result: np.ndarray # array([[2, 0, 7, 5], # [1, 2, 9, 1], # [8, 8, 8, 2], # [4, 3, 6, 9]])
Figure 2.12. Inner 4x4 elements¶