PYTHON

numpy indexing arrays

import numpy as np

# create numpy array
arr = np.array([1, 2, 3, 4, 5])

# first element of array
print('1st element of array arr[0]: ', arr[0])

# 2d array
arr = np.array([[1, 2, 3, 4, 5], [6, 7, 8, 9, 10]])
print('2nd element on 1st row: ', arr[0, 1])

indexing a numpy array in python

array = [[0  1  2  3  4  5] 
  [6 7 8 9 10 11]
  [12 13 14 15 16 17]
  [18 19 20 21 22 23]
  [24 25 26 27 28 29]
  [30 31 32 33 34 35]]
array[0, 3:5]  =  [3 4]

array[4:, 4:] = [[28 29],
             [34 35]]

array[:, 2] =  [2 8 14 20 26 32]

array[2:;2, ::2] = [[12 14 16],
                [24 26 28]]

numpy indexing

>>> x = np.array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
>>> x[1:7:2]
array([1, 3, 5])