Array

Question 1

any?

Answer 1

Returns true if any of the values in the block evaluates to true.

Example:

[1, 2, 3].any? { |num| num.odd? }
=> true

Question 2

assoc, #rassoc

Answer 2

.assoc(obj) earches through an array whose elements are also arrays.
If the first element of the array matches obj it will return the whole array.
Otherwise it returns nil.

.rassoc(obj) does the same for the second element.

arr = [[1, 2], [3, 4], [5, 6]]
arr.assoc(3)

=> [3, 4]

Question 3

reject

Answer 3

Same as .select but it selects values that evaluate to false.

Question 4

take

Answer 4

Takes the number (say 2 or whatever) given as an argument and returns the first 2 or whatever elements in the array.

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

arr.take(3)

=> [1, 2, 3]

Question 5

drop

Answer 5

Opposite it #take as in it drops the first given number of elements and returns the rest.

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

arr.drop(2)

=> [3, 4, 5]

Question 6

inject, #reduce (aliases)

Inherited from Enumerable module

Answer 6

Given an array, they compute all the elements: (5..10).inject(:*)
=> 151200

Can also supply an initial counter
(5..10).reduce(1)
=> 46

If initial counter is not supplied the first element in the collection is the initial counter.

%w[cat fox bear].inject do |memo, word|
memo.length > word.length ? memo : word
end

=> “bear”

Question 7

index #rindex

Answer 7

.index returns first element of array that’s equal to the argument specified:

[“a”, “b”, “c”].index(“b”)

=> 1

.rindex returns the last element in array that matches the argument:

[“a”, “b”, “b”, “c”].rindex(“b”)

=> 2