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Session 0 - Learning Ruby

As most of our participants are not familiar with Ruby, we have created some exercises to learn and practice Ruby syntax - covering conditional statements (if, else, elsif), different ways of iteration (each, select, map) and basic object oriented code (defining and using class, instance functions).

If you have studied any other programming language - the exercises are about translating known concepts to Ruby and should be easy.

If concepts like variable, function and class are new to you, you might require a gentler introduction to programming before learning Rails. You can refer to books on programming or websites like TryRuby and Learn Ruby the Hard Way.

Read the installation guide and setting up local workspace to get started.

Fizz Buzz

Fizz Buzz is a word game for children to teach them about division.

We will use it to learn about transforming traditional C-like for loops into ruby code and a bit of error handling.

The rules of the game are as follows:

  • The first player says the number "1".
  • Each subsequent player counts upwards in turn.
  • Numbers divisible by 3 are replaced by the word "Fizz"
  • Numbers divisible by 5 are replaced by the word "Buzz"
  • Numbers divisible by both 3 and 5 are replaced by the word "FizzBuzz"

For example, a round of Fizz Buzz would go as follows:

1, 2, Fizz, 4, Buzz, Fizz, 7, 8, Fizz, Buzz, 11, Fizz, 13, 14, FizzBuzz,
16, 17, Fizz, 19, Buzz, Fizz, 22, 23, Fizz, Buzz, 26, Fizz, 28, 29,
FizzBuzz, 31, 32, Fizz, 34, Buzz, Fizz, ...

We will take a look at generalization of Fizz Buzz - instead of numbers divisible by 3 or 5, we will let the user decide. They are denoted by keyword arguments x and y.

The first keyword argument n represents the number of turns.

We will be returning an array of strings, containing what each player says on their turn.

For example, fizz_buzz(n: 6, x: 2, y: 3) should return the following: ["1", "Fizz", "Buzz", "Fizz", "5", "FizzBuzz"]

What happens if the function is called by x (or y) = 0 or negative?

The divisiblity by zero is not defined and neither do the little children know how to divide by negtive numbers.

We will raise an ArgumentError exception to let the caller know that their arguments were incorrect.

Implement the function fizz_buzz in the file fizz_buzz.rb and test your code with ruby fizz_buzz_test.rb.

Word Processing

You are writing for a group that uses Machine Learning techniques to read and summarize books and articles into smaller texts while retaining the meaning.

Since the technique works only on lower case words, you want to write two functions lower_case(words) and lower_case!(words) which transform an array of words (representing contents of an article) into all lower case characters. The function lower_case returns an copy of the original array, transforming upper case to lower case characters whereas the function lower_case! modifies the array in-place.

words = ['', 'HELLO', 'WoRlD', 'nice']

lower_case(words) # returns ['', 'hello', 'world', 'nice']
puts words # ['', 'HELLO', 'WoRlD', 'nice']

lower_case!(words) # returns nil
puts words # ['', 'hello', 'world', nice']

The technique relies on prefix of words, you want to implement words_with_prefix(prefix, words) which returns an array containing only words that have the same prefix.

words_with_prefix('apple', ['apple', 'ball', 'applesauce']) # returns ['apple', 'applesauce']

To eliminate redundant words (and thus compressing the text), you define similarity score between two words as the length of the largest common prefix between the words. The function similarity_score takes two words and returns the similarity score.

similarity_score('bike', 'bite') # 2, as 'bi' is the largest common prefix.
similarity_score('apple', 'bite') # 0, as there are no common letters in the prefixes.

To find the best possible match for a word from a given list of words (and retaining the meaning as far as possible), you choose the word with the maximum similarity score. The function most_similar_words(chosen_word, words) find the best possible match(s) for the chosen word.

most_similar_words('apple', ['ball', 'applesauce', 'bike']) # returns ['applesauce']
most_similar_words('apple', ['ball', 'applesauce', 'bike', 'apple']) # returns ['applesauce', 'apple]

Implement the functions described above in the file word_processing.rb and test your code with ruby word_processing_test.rb.

BuySell

You are working for an e-commerce company Buy-n-Sell and working on their inventory functionality.

The items sold by the company are represented by the class Item. An Item stores the following information:

  • Name of the item.
  • Price of the item.
  • The category item belongs to.
  • The discount rate if the item is on sale.
  • The time when the sale ends.

You want to store quantity of the item too, so the company can keep track of items which need to be re-stocked.

To help the company in analyzing their inventory, you come up with the following metric:

  • An item is discounted if the discount deadline has not been yet crossed.
  • The current price of a discounted item is price * (100 - discount rate ) /100.
  • The current price of an regular item is same as price.
  • The stock price of item is defined as the product of current price and quantity.
  • The stock price of a category is sum of individual stock prices of item belonging to the category.

The function stock_price_by_category(items) takes an array of items and calculates the stock price of all categories.

Implement the class Item above in the file item.rb and test your code with ruby item_test.rb.

Interactive Console

You can use the interactive ruby (irb) to help understand and debug your code. irb is similar to python's interactive console and lets you run any ruby code.

For example, to debug fizz_buzz.rb do the following:

  • Open a ruby console using irb.
  • Include the ruby program using require_relative 'fizz_buzz'.
  • Execute the function (or any valid ruby statement using the interpreter).

Debugging