Selecting a sub array from a NumPy array (Slicing)
To get a sub-array, we pass a slice in place of the element index.
Syntax:
numpyArr[x:y]
Here x and y are the starting and last index of the required sub-array.
Example:
Python3
import numpy as np # NumPy Array numpyArr = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9]) # the slice 3:6 is passed instead # of index print("Sub-Array=", numpyArr[3:6]) |
Output:
Sub-Array= [4 5 6]
A sub-array starting from the 3rd index up to the 6th index ( excluding the last the 6th index ) was selected. You can slice a sub-array starting from the first element by leaving the starting index blank.
Example: The following code selects a sub-array starting from the first element.
Python3
import numpy as np numpyArr = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9]) # works same as 0:6 print("Sub-Array=", numpyArr[:6]) |
Output:
Sub-Array= [1 2 3 4 5 6]
Similarly, leaving the left side of the colon blank will give you an array up to the last element.
Example: The following code selects a sub-array starting from a particular index up to the last index.
Python3
import numpy as np numpyArr = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9]) # same as 3:9 or 3:n, where n is # the length of array print("Sub-Array=", numpyArr[3:]) |
Output:
Sub-Array= [4 5 6 7 8 9]
Select an element or sub array by index from a Numpy Array
The elements of a NumPy array are indexed just like normal arrays. The index of the first element will be 0 and the last element will be indexed n-1, where n is the total number of elements.