Ruby Intro - Arrays

Question 1

What do you use to select a range of items from an array set? Difference between the two syntaxes?

Answer 1

Ranges. “..” gives entire range while “…” leaves out the last item in the range.

Question 2

How do you specify last (or second to last, etc.) value when getting a range of elements?

Answer 2

-1 gives last value. -2 gives second to last. Can be noted like so: “3..-1”

Question 3

What’s the syntax for an iterator to access all elements in an array? (3 lines)

Answer 3

cool_things = [“race cars”, “lasers”, “aeroplanes”]

cool_things.each do |cool_thing|
puts “I like #{cool_thing}!”
end

# prints: I like race cars!
#         I like lasers!
#         I like aeroplanes!

Question 4

What is &laquo_space;called when used for inserting into arrays? The _____ ________.

Answer 4

The Shovel Operator

Question 5

Concatenate two arrays into a new one without modifying the originals?

Answer 5

new_array = array1 + array2

Question 6

Concatenate arrays AND modify original

Answer 6

use the concat method

Question 7

three ways to find number of elements in an array. The last way only tells True/false whether array has elements.

Answer 7

“.length” “.count” “.empty?” (empty gives True or False)

Question 8

For arrays, what is a Stack? What methods are used to treat an array like a Stack?

Answer 8

Has LIFO features.
Using push and pop and delete.
Pop will take out an item and also delete it from the array at the same time (does not need print. Printing is just for humans!)
POP acts like DELETE! It also does not print the popped item.

Question 9

For arrays, what is a Queue. What methods are used to treat like a Queue?

Answer 9

Has FIFO features. Using push and “delete_at(0)”

nums = []
nums << 1
nums << 2
nums << 3
nums.delete_at(0)
# => 1
nums
# => [2, 3]

Question 10

What is Array shift and unshift?

Answer 10

Shift is like “delete_at(0)” but also prints the item deleted. Unshift ADDS.

array = [1,2,3,4]
array.shift
# => 1

array
# => [2,3,4]

array.unshift(5)
# => [5,2,3,4]

Question 11

in a single code line, create a sentence that expresses an array string (separated by commas) within the sentence. What is the method used to separate elements in the array?

Answer 11

“I like #{cool_things.join(“, “)}.”

Question 12

What is the “, “ argument to join strings together called?

Answer 12

separator

Question 13

What is method used to find out whether an array contains a specific object/element?

Answer 13

.include?( )

small_primes = [1, 2, 3, 5, 7, 11]
small_primes.include?(9)
# => false

Question 14

How to find the position of first occurence of a specific object/element in an array?

Answer 14

.index( )

small_primes = [1, 2, 3, 5, 7, 11]
small_primes.index(3)
# => 2
small_primes.index(9)
# => nil

Question 15

Code to sort to a new array without changing the original array?

Answer 15

regular “sort”

arr = [3, 2, 1]
sorted_arr = arr.sort
sorted_arr # => [1, 2, 3]
arr # => [3, 2, 1]

Question 16

How do you sort an existing array?

Answer 16

“.sort!”

arr = [3, 2, 1]
arr.sort!
arr # => [1, 2, 3]

Question 17

what are safe and unsafe methods?

Answer 17

unsafe methods are faster but change the original object and end with “!” Always use safe as default unless there is specific reason to use unsafe

Question 18

Method to randomly reorder elements in an array?

Answer 18

.shuffle

Question 19

Method to select/print the first or last element in an array?

Answer 19

.first or .last will select/print it

Question 20

Method to select one random element from an array?

Answer 20

.sample wil select/print it

die = [1,2,3,4,5,6]
die.sample
roll = die.sample

Question 21

Two rules for best naming arrays?

Answer 21

1. Pluralize array name where possible
2. Be expressive with the name instead of terse and algebraic

fancy_car_brands = ["Maserati", "Porsche", "Tesla"]
junk_models = ["Chevy Nova", "Ford Pinto"]

fancy_car_brands.each do |fancy_car_brand|
junk_models.each do |junk_model|
puts “#{fancy_car_brand} would never make junk like the #{junk_model}”
end
end

Question 22

What is a heterogenous array? Are these good or bad?

Answer 22

an array with different data types. This is generally bad. Use homogenous arrays.

Question 23

Two ways to push/shovel multiple elements into an array in a single line of code?

Answer 23

sample.push(3, 4, 5)
# or
sample &laquo_space;3 &laquo_space;4 &laquo_space;5

Question 24

What is the method that returns an array with duplicates removed? How does it work?

Answer 24

.uniq. This creates a temporary new array that has duplicates removed
bonus: .uniq! removes duplicates from original array

Question 25

What is it called when you add your new method to an Array class? How do you do this?

Answer 25

Monkey patching.
It is frowned upon. But here’s how:

class Array
  def my_uniq
    # ...
  end
end

Question 26

3 ways to create a new array of a range of numbers

Answer 26

You can create an array with a range using splat (BEST WAY),
» a=*(1..10)
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

using the Array constructor,
Array (1..10)
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

or using to_a
(1..10).to_a
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Question 27

For arrays, how are “shift” and “delete_at(0)” different?

Answer 27

shift prints the item deleted.

delete_at(0) does not print.

Question 28

Four ways to convert string into array letters. One other way to convert to separate words array.

Answer 28

text. split(//)
text. scan(/./)
text. chars.to_a
text. each_char.to_a

text.split()

Question 29

super simple Code for converting all elements in an array into an integer/string etc.?

Answer 29

array.map(&:to_i)