WORKING WITH “–1” SUBRANGES WITH ARRAYS

Listing 2.11 displays the content of np2darray2.py that illustrates how to compute exponents of the elements in a NumPy array.

LISTING 2.11: np2darray2.py

import numpy as np

# -1 => "the last element in …" (row or col)

arr1  = np.array([(1,2,3),(4,5,6),(7,8,9),(10,11,12)])
print('arr1:',        arr1)
print('arr1[-1,:]:',  arr1[-1,:])
print('arr1[:,-1]:',  arr1[:,-1])
print('arr1[-1:,-1]:',arr1[-1:,-1])

Listing 2.11 contains a NumPy array called arr1 followed by four print() statements, each of which displays a different subrange of values in arr1. The output from launching Listing 2.11 is here:

(arr1:', array([[1,  2,  3],
                [4,  5,  6],
                [7,  8,  9],
                [10, 11, 12]]))
(arr1[-1,:]]',   array([10, 11, 12]))
(arr1[:,-1]:',   array([3,  6,  9, 12]))
(arr1[-1:,-1]]', array([12]))