Ranges

Introduction

You should finish all of the Week 1 Problem sets before moving on to this section!

Checkout the Range Documentation. Bookmark this page! Look at the "Methods" column on the left-hand side.

Ranges can be used to represent a set of integers or characters. For example, lets say you wanted to create an alphabet. You'll need a collection of all the characters from "a" - "z". Well, you could use an array..

alphabet = ["a", "b", "c", ... "z"]

but this process is quite annoying. We don't want to have to type out 26 different characters. Behold, the alphabet range:

alphabet = ("a".."z")

And that's it! Ruby knows how to fill in the middle characters for us. All we have to do is specify the upper and lower bounds of the range. Want to know the 16th letter in the alphabet?

alphabet = ("a".."z").to_a # converts range to an array!
puts alphabet[15] # ==> "p"

Creating Ranges

Ranges are made by wrapping a lower and upper bound in parentheses and including 2 or 3 dots in between. The number of dots specifies whether the range is inclusive or exclusive.

Inclusive Ranges

Inclusive ranges are defined using two dots: (? .. ?). Below are some examples of inclusive ranges and the values they represent:

abc = ("a".."c") # ==> a - c
digits = (0..9)  # ==> 0 - 9

Inclusive ranges include the upper bound. In the above examples, both "c" and 9 are included in their respective ranges.

Exclusive Ranges

Exclusive ranges are defined using 3 dots: (? ... ?).

letters = ("d"..."q") # ==> d - p
digits = (1...5)      # ==> 1 - 4

Exclusive ranges exclude the upper bound.

#to_a

We cannot directly index a range:

alphabet = ("a".."z")
alphabet[15] # throws error!

Instead, we can convert a range into an array using the to_a method. Doing so allows us to index the collection and ask for specific values.

alphabet = ("a".."z").to_a
alphabet[10] # ==> "k"

#each

Just like arrays, ranges have an #each method. This method allows us to execute a code block -- perform some action -- for each element in the range. If we wanted to print every letter of the alphabet...

("a".."z").each do |letter|
  puts letter
end

Note the we don't have to convert the range to an array in order to use the #each method.