Cheat Sheet Content for working with Enumerables

1. What do we want to know about Enumerables?

The Enumerable is a module and its mixin provide collection classes with methods to traverse, search, sort & manipulate collections.

Modules are a way of grouping together methods, classes, and constants. Modules give you two major benefits.

Enumberable is a module that can be used as a mixin the following classes: Hashes, Arrays, Sets, Ranges, & Structs.

2. What would be good to have on hand when working Enumberables?

Commonly used Enumberable Methods -

cycle:

Kind of like each, but you can run the code block multiple times, if no argument is given, it runs forever.

arr = ["a", "b", "c"]
arr.cycle { |x| puts x }  # print, a, b, c, a, b, c,.. forever.
arr.cycle(2) { |x| puts x }  # print, a, b, c, a, b, c.

each_slice:

Cuts the array into slices based on the argument.

(1..10).each_slice(3) { |slice| p slice }
# outputs below
[1, 2, 3]
[4, 5, 6]
[7, 8, 9]
[10]

max_by:

Find something in the array by stating the criteria in the code block. 

arr = [albatross, dog, horse]
arr.max_by { |x| x.length }   #=> "albatross"

If the n argument is given, minimum n elements are returned as an array. 

arr = [albatross, dog, horse]
arr.max_by(2) {|x| x.length } #=> ["albatross", "horse"]

drop:

If an argument n is given, drop deletes the first n elements in the array. 

arr = [1, 2, 3, 4, 5, 0]
arr.drop(3)             #=> [4, 5, 0]

drop_while:

Delete all elements in an array that fits the criteria stated in the code block. 

arr = [1, 2, 3, 4, 5, 0]
arr.drop_while { |i| i < 3 }   #=> [3, 4, 5, 0]

partition:

Returns two arrays, the first containing the elements of array for which the block evaluates to true, the second containing the rest. 

partition: { |obj| block } → [ true_array, false_array ]

(1..6).partition { |v| v.even? }  #=> [[2, 4, 6], [1, 3, 5]]

grep:

Return all the values in a collection that matches the pattern given in the argument. 

(1..100).grep(38..44)   #=> [38, 39, 40, 41, 42, 43, 44]

3. ENUMBERABLE is ruby's way of saying that we can get elemenents our of a collection one at a time.

Definition: Enumerate - mention number of things, one by one.

The Enumberable module itself doesnt define the #each method. It's responsiblity of the class that is including this module to do so.

4. What is the point of returning and Enumerator?

Using an Enumerator vs an Array: for an Enumerator you can go through this set of collections one by one. As oppose to an Array where you would have to break the the collection.