Array Methods

Overview

This lesson will present some useful methods you can use when working with arrays.

Objectives

1. Sort arrays with the sort method

2. Find the first and last elements of an array

3. Find the size of an array

4. Find if an element is in the array with the include? method

Working With Arrays

The .sort Method

This method rearranges the contents of the array by sorting them. For strings, this means alphabetically, for numerical values, this means from smallest number to highest number.

Advanced: ​The​ .sort ​method works by implicitly comparing elements with the "spaceship" operator​ <=> ​*(because it looks like a flying saucer, swoosh!) and moving them accordingly.*​

famous_cats = ["lil' bub", "grumpy cat", "maru"]
famous_cats.sort
  => ["grumpy cat", "lil' bub", "maru"]

One thing to be aware of is that the return value of famous_cats remains unchanged after using the sort method on it. Meaning if you call famous_cats again after the sort, it will still return ["lil' bub", "grumpy cat", "maru"], not the previously sorted array.

Because sort returns a new array, we generally store it into another variable. So we would do sorted_cats = famous_cats.sort. Now we have two copies of the array. One unsorted (famous_cats) and one sorted (sorted_cats). If you don't care about the unsorted version of the array you can call sort!. This will sort the existing array without requiring you to save the return into a new variable. You'll notice the !. It's a ruby convention that a method with the ! will do the operation in place. It will modify the receiver of the method (AKA the thing to the left of the dot).

The .reverse Method

This method reverses an array.

famous_wizards = ["Dumbledore", "Gandalf", "Merlin"]
famous_wizards.reverse
  => ["Merlin", "Gandalf", "Dumbledore"]

Similarly to sort!, you can call reverse!, again modifying the receiver of the method in place.

The .include? Method

This method will return a boolean of whether or not the array contains (or ​includes​) the element submitted to it inside the parentheses:

famous_cats = ["lil' bub", "grumpy cat", "Maru"]
famous_cats.include?("Garfield")
  => false
famous_cats.include?("Maru")
  => true

Since we are just returning true or false, the receiver of the method, famous_cats, remains unchanged.

The .first Method

This method will return the first element of the array, as its name suggests. Again, it does not change the return value of the original array.

famous_cats = ["lil' bub", "grumpy cat", "Maru"]
famous_cats.first
  => "lil' bub"

The .last Method

This method will return the last element of the array, as its name suggests. Again, it does not change the original array.

famous_cats = ["lil' bub", "grumpy cat", "Maru"]
famous_cats.last
  => "Maru"

The .size Method

This method will return the number of elements in the array.

famous_cats = ["lil' bub", "grumpy cat", "Maru"]
famous_cats.size
  => 3

Even though arrays start with a 0 index, this method returns the actual number of elements, starting from 1.

Note: Be aware that all of the methods we have covered in this reading are case sensitive. For example, reverse not Reverse.