We'll explore Ruby's Array type and some of its methods. We'll also have a look at a few ways in which Ruby makes list processing (iterating through arrays) a bit more fun for the developer.

List processing is at the core of most web development tasks, so practicing it in Ruby (and later, comparing it to JavaScript), will illuminate the logical features of list processing tasks in addition to implementation specifics.

• ga-wdi-boston/js-array-methods
• ga-wdi-boston/ruby-vs-js-arrays

By the end of this, developers should be able to:

• Use Ruby array methods to iterate through arrays.
• Pass inline code as blocks to Array instance methods.
• Pass method names as symbols to Array instance methods.

1. Fork and clone this repository.
2. Make a new branch, training.
3. Install dependencies with bundle install.

Both JavaScript and Ruby have types that represent lists. In both languages, these types are called "arrays". In Ruby, Array is a class that holds methods for arrays, and in JavaScript, Array.prototype is an object that holds methods for arrays.

Let's compare the list of methods for Array in each language. Here is some documentation for reference:

• Array.prototype - JavaScript | MDN
• Class: Array (Ruby 2.3.0)

Let's explore Ruby's map method.

# in irb or pry
fibs = [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

How can we use map to multiply each member of fibs by two in Ruby?

# fibs.map { |fib| ... } for single-line, or

fibs.map do |fib|
  # something here
end

Let's use reduce to calculate the sum of elements in fibs.

In JavaScript, we used a function to control the behavior of Array methods. In Ruby, we use a block ( { |p| ... } for one line blocks, do ... end for multi-line blocks).

In Ruby, write scripts, in lib/fibonacci.rb.

• calculates the product of elements of fibs (excluding zero).
• calculates the sum of the odd elements of fibs
• calculates the product of the even elements of fibs(excluding zero).

Let's use the script bin/people_array.rb to explore Array methods in Ruby. The data in the objects we'll be processing comes from the comma separated values (CSV) file data/people.csv.

The Person objects we'll test against have properties/methods that align with the headers in data/people.csv plus the method age.

Use the bin/people_array.rb script to

• Count all the people who are older than you (or just pick an age).
• Count all the people who are younger than you (or just pick an age).
• Count all the people whose first name and last name start with the same letter.
• Calculate the average age of all the people.

The results of the Ruby Array methods -, &, |, and flatten aren't easily reproducible in JavaScript.

• - is an Array Difference
• & is a Set Intersection
• | is a Set Union
• flatten reduces dimension

We'll explore these methods using bin/sets_etc.rb.

Remember our text analysis exercise from way-back?

Let's implement normalize_words, unique_words, word_count, and word_frequencies in lib/string.rb

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