Ruby Cheatsheet - Jesus Castello

Question 1

Strings

Answer 1

A string is a sequence of characters inside two quotation marks (“”). Used to represent text & data. Also can use single quotation marks (‘’).

Question 2

Important methods for Strings

Answer 2

• size
• empty?
• include?
• gsub
• split

Question 3

Hashes

Answer 3

A hash ( {} ) is a key-value pair ( a => b) data structure. Used as a dictionary. You can access hash elements by their keys. Keys are unique.

Question 4

Important methods for hashes

Answer 4

• key?
• fetch
• new (for default value)
• merge

Question 5

Hash example

Answer 5

#Create
h = { a: 1, b: 2, c: 3 }
#Access
h[:a]
# Set
h[:test] = 10

Question 6

Symbol

Answer 6

A static string used for identification, one common example is hash keys. They always start with a colon ( :bacon). Symbols are never used for their content (the individual characters).

Question 7

nil

Answer 7

A singleton class (only one object allowed) that represents a default or “not found” kind of value.

Evaluates to “false” in a conditional context.

Question 8

Array

Answer 8

An object used to represent a list of objects. An array can contain any kind of object ( a = [1, “abc”, []] ), including other arrays.

You access array elements with their index ( a[0] ) & nested arrays with a[0][0] .

Question 9

Important methods for Array

Answer 9

• size
• empty?
• push / pop
• join
• flatten

Question 10

Enumerable

Answer 10

A Ruby module used to iterate over the elements of any class that implements the each method, like Array, Range & Hash.

Question 11

Important methods for Enumerable

Answer 11

• map
• select
• inject

Question 12

Method count

Answer 12

exactly what the name says, count things that evaluate to true inside a block

Question 13

method map

Answer 13

Transforms every element of the enumerable object and returns the new version as an array

Question 14

FILE

Answer 14

A class that helps you work with files in Ruby. Anything from reading them, writing to them or even getting info about them, like the file size.