Mixed Ruby revision

Question 1

Which operator returns a new array containing the elements common to both values, without duplicates?

Answer 1

The & operator

Question 2

Which operator returns a new array by joining arrays and removing duplicates?

Answer 2

The | operator

Question 3

Which method returns a new array containing the original array elements in reverse order?

Answer 3

The reverse method (e.g. array.reverse)

Question 4

Reverse the order of the elements in the array below:

elements = [1, 3, 5, 7, 9]

Answer 4

elements.reverse

NB If you use the reverse method without (!) and don’t save it to a new variable, it will just reverse it once and keep the original value.

Question 5

Which 2 methods return the number of elements in an array?

Answer 5

array.length or array.size

NB you can also use .count with no arguments passed to it and it will perform the same way as these on arrays. It’s not the same as these two though (.length and .size can be used interchangably) - you can do more with .count by passing it arguments. You also cannot use .count on a string without an argument.

Question 6

Which method returns a new array with the elements sorted?

Answer 6

array.sort

Question 7

Which method returns a new array with duplicate values removed from the array?

Answer 7

array.uniq

(array.uniq! removes duplicates in place.)

Question 8

Which method safeguards an array, preventing it from being modified?

Answer 8

array.freeze

Question 9

Which method returns true if an object is present in an array and false otherwise?

Answer 9

array.include?(obj)

Question 10

Which method returns the element with the minimum value in an array?

Answer 10

array.min

Question 11

Which method returns the element with the maximum value in an array?

Answer 11

array.max

Question 12

How could you iterate over an array of elements and puts each element to the console, with a for loop?

Answer 12

array = [“apple”, “dragonfruit”, “plum”]
for x in array
puts “Value: #{x}” # alternatively, puts x
end

Question 13

How would you access the value associated with “Lena” within the following hash?

ages = { “Marge” => 28, “Lena”=> 19, “Hamish” => 42 }

Answer 13

ages[“Lena”]

Question 14

Why use symbols instead of strings as hash keys?

Answer 14

Using symbols not only saves time when doing comparisons, but also saves memory, because they are only stored once.

Question 15

Create a hash (h) containing a key (name) and its value (“Flora”). Show 2 ways of doing this.

Answer 15

h = {name: “Flora”} # This method is shorter!

h = {:name => “Flora”}

Question 16

Which method removes a key-value pair from a hash by key?

Answer 16

hash.delete(key)

Question 17

Which method returns the key for a given value in a hash or nil if no matching value is found?

Answer 17

hash.key(value)

Question 18

Which method creates a new hash, reversing keys and values from the original hash? i.e., in the new hash, the keys from the original hash become values and values become keys

Answer 18

hash.invert

Question 19

Which method returns a new array containing all the keys from a hash?

Answer 19

hash.keys

Question 20

Which method returns a new array containing all the values from a hash?

Answer 20

hash.values

Question 21

Which method returns the length of a hash as an integer?

Answer 21

hash.length

Question 22

Which method mergers two hashes together?

Answer 22

hash.merge

e.g. hash_a.merge(hash_b)

Question 23

round down a float and convert it to an Integer,
# so 9.52 becomes 9
def round_down_number(float)
# YOUR CODE HERE
end

Answer 23

def round_down_number(float)
float.to_i
end

Question 24

What method allows you to filter an array of objects by selecting those that meet a true or false condition?

Answer 24

.select

Remember, it needs a block with a statement that evaluates to true or false, e.g.

array = [1, 2, 3, 4, 5, 6]
array.select {|num| num.even? }

Question 25

Combine .select with another method to filter the array to select every other fruit.

fruits = %w(apple orange banana)
# YOUR CODE HERE
# [“apple”, “banana”]

Answer 25

fruits = %w(apple orange banana)
fruits.select.with_index { |word, idx| idx.even? }
# [“apple”, “banana”]

Question 26

What method allows you to filter an array of objects by rejecting something you don’t want to include?

Answer 26

.reject

It’s the opposite of .select (you can use .select with a not statement for the same purpose but .reject can help keep your code clear).

Question 27

[1, 3, 5]

Use .reject to filter the following array so that no even objects are included.

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

Answer 27

array = [1, 2, 3, 4, 5]
array.reject {|num| num.even? }

Question 28

Combine the .reject method with other methods to filter the following array so that no objects containing a 5 are included.

i.e. if you are given an array of numbers, you should return an array that contains no 5 in any digit of any number.

array = [1, 2, 3, 4, 5, 15, 20, 50]
# [1, 2, 3, 4, 20]

Answer 28

array = [1, 2, 3, 4, 5, 15, 20, 50]
no_fives_array= array.reject {|num| num.to_s.include?(“5”)}