Python Libraries For Data Science

NumPy Creating Arrays

Exploring few examples on 2D Array
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2 D Array

import numpy as np

arr1=np.array([1,2,3])
arr1

OUTPUT:

array([1, 2, 3])
type(arr1)

OUTPUT:

numpy.ndarray‍
arr1.ndim

OUTPUT:

1

arr1.size

OUTPUT:

3

arr1.shape
(3,)

Creating 2-D Array

arr = np.array([    [1,1,1]  ,[2,2,2]   ,[3,3,3]  ,   [4,4,4]    ])
print(arr)

OUTPUT:

[[1 1 1]
[2 2 2]
[3 3 3]
[4 4 4]]


arr.shape

OUTPUT:

(4,3)
arr.size

OUTPUT:

12
arr.ndim

OUTPUT:

2

Class and Attributes of nd array,Size and shape of a numpy array

list3 = [ [1, 2, 3, 4],[5, 6, 7, 8], [9, 10, 11, 12] ]

arr = np.array(list3, dtype ='str')
print(arr)

OUTPUT:

[['1' '2' '3' '4']
['5' '6' '7' '8']
['9' '10' '11' '12']]

arr.dtype

OUTPUT:

dtype('<U2')
arr.size

OUTPUT:

12

arr.ndim

OUTPUT:

2

Accessing 2-D array Indexing

list3 = [[1, 2, 3, 4],[5, 6, 7, 8], [9, 10, 11, 12]]

arr = np.array(list3)

print(arr)

OUTPUT:

[[ 1  2  3  4]
[ 5  6 7  8]
[ 9 10 11 12]]

arr[ 0:2 , 2:4 ]

OUTPUT:

array([[3, 4],
      [7, 8]])

print("First Row:",arr[0])
print("Last Row:",arr[-1])
print("Single Element",arr[2,3])
print("All Rows but Second colums",arr[:,2])
print("Second Row and all colums",arr[2,:])
print("All rows but only columns from 1 to 3\n",arr[:,1:3])

OUTPUT:

First Row: [1 2 3 4]
Last Row: [ 9 10 11 12]
Single Element 12
All Rows but Second colums [ 3  7 11]
Second Row and all colums [ 9 10 11 12]
All rows but only columns from 1 to 3
[[ 2  3]
[ 6  7]
[10 11]]

Lesson Assignment
Challenge yourself with our lab assignment and put your skills to test.
# Python Program to find the area of triangle

a = 5
b = 6
c = 7

# Uncomment below to take inputs from the user
# a = float(input('Enter first side: '))
# b = float(input('Enter second side: '))
# c = float(input('Enter third side: '))

# calculate the semi-perimeter
s = (a + b + c) / 2

# calculate the area
area = (s*(s-a)*(s-b)*(s-c)) ** 0.5
print('The area of the triangle is %0.2f' %area)
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