Ruby Arrays And Hashes


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Arrays

Arrays are ordered, integer-indexed collections of any object.


# This is an array
array = [1, 2, 3, 4, 5] #=> [1, 2, 3, 4, 5]

# Arrays can contain different types of items    
[1, "hello", false] #=> [1, "hello", false]

# Arrays can be indexed
# From the front
array[0] #=> 1
array[12] #=> nil

# From the end
array[-1] #=> 5

# With a start index and length
array[2, 3] #=> [3, 4, 5]

# Or with a range
array[1..3] #=> [2, 3, 4]

# Like arithmetic, [var] access is just syntactic sugar
# for calling a method [] on an object
array.[] 0 #=> 1
array.[] 12 #=> nil

# Add to an array with <<
array << 6 #=> [1, 2, 3, 4, 5, 6]

#Lots of methods for getting info about an Array
array.length #=> 6
array.first #=> 1
array.last #=> 6

array.include?(3) #=> true
array.include?(9) #=> false

Hashes

A Hash is a dictionary-like collection of unique keys and their values.


# Hashes are denoted with curly braces:
hash = {'color' => 'green', 'number' => 5}

hash.keys #=> ['color', 'number']
hash.values #=> ['green', 5]

# Hashes can be quickly looked up by key:
hash['color'] #=> 'green'
hash['number'] #=> 5

# Asking a hash for a key that doesn't exist returns nil:
hash['missing'] #=> nil

# Since Ruby 1.9, there's a special syntax when using symbols as keys:

new_hash = { defcon: 3, action: true}    
new_hash.keys #=> [:defcon, :action]

Tip: Both Arrays and Hashes are Enumerable. They share a lot of useful methods such as each, map, count, and more

Challenge

What will the following code return?

array = [1, 2, 3, 4, 5]
array[1..2]

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Challenge

You will be given an array of numbers ar. Create and print another array of length 2 that just contains the first and last number in the original array.

(Note: To print an array ar, just use print ar. To print a newline, use "\n".)

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