Introducing arrays

Introduction to NumPy

Izzy Weber

Core Curriculum Manager, DataCamp

NumPy and the Python ecosystem

A graphic of Atlas holding up the globe, styled as NumPy since NumPy holds up the Python world

Introduction to NumPy

NumPy arrays

 

graphics of 1D, 2D, and 3D arrays

Introduction to NumPy

Importing NumPy

 

import numpy as np
Introduction to NumPy

Creating 1D arrays from lists

python_list = [3, 2, 5, 8, 4, 9, 7, 6, 1]
array = np.array(python_list)
array

array([3, 2, 5, 8, 4, 9, 7, 6, 1])

 

type(array)

numpy.ndarray
Introduction to NumPy

Creating 2D arrays from lists

python_list_of_lists = [[3, 2, 5],
                        [9, 7, 1],
                        [4, 3, 6]]
np.array(python_list_of_lists)

array([[3, 2, 5],
       [9, 7, 1],
       [4, 3, 6]])
Introduction to NumPy

Python lists

  • Can contain many different data types
python_list = ["beep", False, 56, .945, [3, 2, 5]]

 

NumPy arrays

  • Can contain only a single data type
  • Use less space in memory
numpy_boolean_array = [[True, False], [True, True], [False, True]]

numpy_float_array = [1.9, 5.4, 8.8, 3.6, 3.2]
Introduction to NumPy

Creating arrays from scratch

 

There are many NumPy functions used to create arrays from scratch, including:

  • np.zeros()
  • np.random.random()
  • np.arange()
Introduction to NumPy

Creating arrays: np.zeros()

np.zeros((5, 3))

array([[0., 0., 0.],
       [0., 0., 0.],
       [0., 0., 0.],
       [0., 0., 0.],
       [0., 0., 0.]])
Introduction to NumPy

Creating arrays: np.random.random()

np.random.random((2, 4))

array([[0.88524516, 0.85641352, 0.33463107, 0.53337117],
       [0.69933362, 0.09295327, 0.93616428, 0.03601592]])

 

np.random is a NumPy module while np.random.random()is a function within np.random

Introduction to NumPy

Creating arrays with np.arange()

np.arange(-3, 4)

array([-3, -2, -1,  0,  1,  2,  3])

np.arange(4)

array([0, 1, 2, 3])

np.arange(-3, 4, 3)

array([-3,  0,  3])

from matplotlib import pyplot as plt
plt.scatter(np.arange(0, 7),
            np.arange(-3, 4))
plt.show()

A plot of two range arrays on the X and Y axes

Introduction to NumPy

Let's practice!

Introduction to NumPy

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