Array and Hashes

Question 1

We can put many things in an array, heck we can even put arrays in an array, but what is this called?

Answer 1

This is called multidimensional arrays

Question 2

Create a two dimensional array and print each array on it’s own separate line

Answer 2

my_array = [[‘Scott’],[’Scott’],[‘Scott’], [’Scott’]]

my_array.each { |word| puts “#{word}” }

Question 3

What is a hash?

Answer 3

Create a has using literal notation, and then create a hash the other way (Also print a value from each to console)

Question 4

Create a has using literal notation, and then create a hash the other way (Also print a value from each to console)

Answer 4

me = {
  “name” => “Scott”,
   age => 18,
   virgin => true
}
puts me[“name”]

pets = Hash.new
pets[“Lola”] = “rabbit”
puts pets[“Lola”]

Question 5

Iterate over the following hash, but print out the value (only) to the console

Answer 5

my_hash = {
"Mohit" => "Curry",
"Seb" => "Burritos",
"Scott" => "Kroket"
}

my_has.each do |name, food|
puts food
end

Question 6

If I have a two dimensional array, so an array that contains arrays, how could you print out the items in the sub arrays?

Answer 6

s = [[“ham”, “swiss”], [“turkey”, “cheddar”], [“roast beef”, “gruyere”]]

s.each do |sub_array|
sub_array.each do |food|
puts food
end
end

Question 7

With Hashes, you can assign keys to strings, but how can you assign a key as a symbol? Also write what the key behaviour difference is between the two?

Answer 7

my_hash = {
dog: “Woof”
}

The main difference is that if you have keys listed as a string then multiple of these keys can all have the same value, however with symbols theirs only one particular copy of a given symbol

Question 8

Give three reasons why symbols are good to use as Hash keys?

Answer 8

1. They’re immutable, meaning they can’t be changed once they’re created
2. Only one copy of a symbol exists at any given time, so they save memory
3. They’re faster, because of the above two reasons`

Question 9

How would you convert the following array with strings to a new array with symbols? List the two methods for this conversion.

Answer 9

strings = ["JavaScript", "Ruby", "HTML", "CSS"]
symbols = []

strings.each { |s| symbols.push(s.to_sym) }
print symbols

1. to_sym
2. .intern

Question 10

Create a hash with old syntax and the new 1.9 Ruby syntax

Answer 10

Old:

movies = {
:elf => “Great”,
:Blind_Side => “Fantastic”
}

New:

movies = {
elf: “Great”,
Blind_Side: “Fantastic”
}

Question 11

How would I print out just the key of an array, and just the values?

Answer 11

movies = {
elf: "5",
cars: "4"
}
movies.each_key { |k| puts k, " "}
movies.each_value { |v| puts v, " "}

Question 12

If I have the following array, how could I access just the first three items in the array and how could I access everything BUT the first three?

Answer 12

arr. take(3)

arr. drop(3)

Question 13

With the following array written below, remove all the elements based on true criteria

Answer 13

my_numbers = [2, 6, 5]
odd_numbers = my_numbers.reject { |num| num % 2 == 0 }

Question 14

How to check whether a hash pair has the value of a certain key or not?

Answer 14

movies[movie_name.to_sym].nil?

or

movies.include? movie_name.to_sym

Question 15

How would you delete a key/value pair in the following hash?

movies {
Elf: 5,
Cars: 4
}

Answer 15

movies.reject! { |movie| movie == movie_name.to_sym }

Question 16

With the following array how could you access the last element, not just simply wring out 5 for example because thats the last index of a length of 6. There are two ways, write both.

Answer 16

array[array.length - 1]

array[-1]