Getting Familiar With Ruby Arrays and Hash Methods.

This post is about getting familiar with array and hash methods. Understanding arrays and hashes are very core concepts of Ruby and other frameworks like Rails.

Now lets have some fun with some examples of Array and Hash mehtods.

Given the following array my_array = [1, 2, 3, 5, 7, 9, 11, 12, 13, 15], we are going to iterate over it and print each element to the screen using the each method.

my_array.each { |val| puts val }
1
2
3
5
7
11
12
13
15
=> [1, 2, 3, 5, 7, 9, 11, 12, 13, 15]

It prints every element in the array and returns the entire array at the end.

Next, lets use the select method to select all even elements from my_array. We can do something like this:

my_array.select { |val| val % 2 == 0 }
=> [2, 12]

Or we can do this:

my_array.select { |val| val.even? }
=> [2, 12]

Cute right?

Note: Select returns an array by default, so we didn't have to puts the value like we did with the each method. Also, when using select method, the code within the block or { } evaluates to true or false. So when its true it's going to be selected, if its false it won't be selected.

Finally, lets use the collect method to square the elements of my_array. We can do this:

my_array.collect { |val| val ** 2 }
=> [1, 4, 9, 25, 49, 81, 121, 144, 169, 225]

Note: We can use the map method to achieve the same result.

If we have a hash, how do we get the key and value pairs? We'll use the each method.

club = {name: "man united", titles: 20, manager: "fergie", location: "old trafford manchester"}

club.each { |key, val| puts "key is #{key} value is #{val}" }

# Produces
key is name value is man uinted
key is title value is 20
key is manager value is fergie
key is location value is old trafford manchester

What if we want only the keys from a hash? We'll use the each_key method like so:

club = {name: "man united", titles: 20, manager: "fergie", location: "old trafford manchester"}

club.each_key { |key| puts "key is #{key}"}

# Produces
key is name
key is title
key is manager
key is location

Conclusion: Array and Hash methods are very good to know and this post has covered just a few. Learn more about these methods by looking at several Ruby/Rails APIs.