np-1__numpy-intro.md

Index/ Python Data Analysis

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Numpy

Objective

Learn Numpy

Reference

Essentials (★☆☆)

• Numpy chapter from the excellent open source book Python Data Science Book is an excellent introduction to Numpy
  • Data types
  • Basics of numpy arrays
• Array slicing
  • https://www.w3schools.com/python/numpy_array_slicing.asp - basics
  • https://www.pythoninformer.com/python-libraries/numpy/index-and-slice/ - good graphics

Intermediate (★★☆)

• Numpy axis - Read this and understand how axis work
• From Ch 2 - Numpy from the excellent open source book Python Data Science Book
  • Functions
  • Aggregations
  • Masking
  • Fancy indexing
  • Sorting

Checklist

After completing the exercises below, you should be comfortable with

• Using Numpy

Exercises

Difficulty Level

★☆☆ - Easy
★★☆ - Medium
★★★ - Challenging
★★★★ - Bonus

Basics - Creating and modifying arrays

A1 - Import numpy packge and print out the version (★☆☆)

A2 - Create a Numpy array with these elements [1,3,5,7] (★☆☆)
Hint : np.array

A3 - Add an element 9 to the above array to the end (★☆☆)
Expected output : [1,3,5,7,9]

A4 - Add an element 0 to the above array at the beginning (★☆☆)
Expected output : [0,1,3,5,7,9]

A5 - Create a numpy array of 5 elements. What are the contents of the array (★☆☆)
Hint: np.empty

A6 - Create a numpy array of 5 elements, initialize them to zero (★☆☆)
Hint : np.zero
Expected output: [0,0,0,0,0]

A7 - Change the 3rd element of the above array to 100 (★☆☆)
Expected output: [0,0,0,100,0]

A8 - Create a numpy array of numbers from 1 to 10 (★☆☆)
Hint: np.arange
Expected result: [1,2,3,4,5,6,7,8,9,10]

A9 - Create a random number between and 1 and 100 (★☆☆)
Hint: np.random

Indexing

B1 - Create a numpy array of numbers from 1 to 10. Print the first and last element (★☆☆)
Hint: np.arange , [:0] and [:-1]

B2 - Create a numpy array of numbers from 1 to 10. Print out elements after index 2 (★☆☆)
Hint: np.arange and [2:]
Expected result: [3,4,5,6,7,8,9,10]

B3 - Create a numpy array of numbers from 1 to 10. Print out elements from index 2 to 8 (★☆☆)
Hint: np.arange and [?:?]
Expected result: [3,4,5,6,7]

Searching

C1 - Create an array of 10 length with random numbers between 0 to 100. Print out the maximum and minimum element (★★☆)
Hint: np.random.?, np.max and np.min

C2 - Create an array of 10 length with random numbers between 0 to 100. Print out the index of the maximum element (★★☆)
Hint: np.argmax

For example, if the array is
[10, 12, 7, 33, 88, 42, 40, 25, 8, 50]
the max-index is : 4 (88)

C3 - Create an array as follows [4,-2, 0, 1, 3, -5]. Only print numbers greater than zero (★★☆)
Expected output: [4,3]

Matrix

D1 - Create an array of numbers 1 to 12. Shape the above array into a 4x3 matrix (★★☆)

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

Hint: np.arange and np.reshape

D2 - Create a multi-dimensional 3x3x3 array with random numbers between 1 and 10. Print out the sum of all elemenets (★★☆)
Hint: np.sum

D3 - Create a 4x3 matrix. Initialize it with random numbers between 1 and 10. Print out the sum of numbers per each column and each row (★★☆)
Hint: np.sum

D4 - Create two 3x2 matrices. Join them row wise to create a 6x2 matrix (★★☆)
Hint: np.concatenate

D5 - Create two 3x2 matrices. Join them column wise to create a 3x4 matrix (★★☆)
Hint: np.concatenate

D6 - Create a 4x3 matrix. Splice the matrix into four 1x3 matrices column wise (★★☆)

More Exercices

• https://www.w3resource.com/python-exercises/numpy/basic/index.php - This site has tons of great exercises
• 100 Numpy exercises

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Index/ Python Data Analysis