Enumerators

Question 1

return a new array with each value multiplied by two:

arr = [ 1, 2, 3, 4 ]

Answer 1

arr = [ 1, 2, 3, 4 ]
newArray = arr.map { |x| x * 2 }

Question 2

what is a another name for the MAP method?

Answer 2

COLLECT

Question 3

Return the sum of all values in the given array:

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

Answer 3

nums = [1, 2, 3, 4, 5]
nums.inject(0) do |accum, element| # accum is initially set to 0, the method argument
accum + element
end

Question 4

what is another name for the INJECT method?

Answer 4

REDUCE

Question 5

Return the items from the given range that are divisible by 3:
num = ( 1..10 )

Answer 5

nums = ( 1..10 )
nums.select do | i |
  i % 3 == 0
end 
# ==> [3, 6, 9 ]

Question 6

What is another name for the SELECT method?

Answer 6

FIND_ALL

Question 7

nums = [1, 4, 5, 6, 7 ]

Answer 7

nums.count # ==> 5

Question 8

Does this array contain a 4?
nums = [ 1, 4, 5, 6, 7 ]

Answer 8

nums.include?(4)

Question 9

Does the array contain even numbers?
nums = [2, 3, 5, 7 ]

Answer 9

nums.any? do |x|
x % 2 == 0
end

Question 10

What methods would you use to determine if all or none of the collection equal a value or criteria?

Answer 10

ALL? / NONE?

Question 11

Write a method that finds the median of a given array of integers. If the array has an odd number of integers, return the middle item from the sorted array. If the array has an even number of integers, return the average of the middle two items from the sorted array.

Answer 11

…

Question 12

Create a method that takes in an Array of Strings and uses inject to return the concatenation of the strings.

Answer 12

..

Question 13

How would you write a block given an array of positive integers and return another array with only the values over 100?

Answer 13

arr.select do |x|
x >= 100
end