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Here is my cheat sheet I created along my learning journey. If you have any recommendations (addition/subtraction) let me know.
Naming Conventions
#Snake Case for files
customer_import.rb
#Snake Case for Methods, Variables and Symbols
first_name = 'Mike'
def display_customer
# some code
end
:light_red
#Screaming Snake Case for Constants
API_KEY = '123ABC'
#CapitalCase for Classes and Modules
class ProductManager
# some code
end
module CustomerSupport
# some code
end
Variables declaration
# string
full_name = 'Mike Taylor'
# integer
count = 20
# float
book_price = 15.80
# booleans
active? = true
admin_user? = false
#Array
fruits = ['Appel', 'Orange', 'Banana']
#Hash
fruit_color = { apple: 'red' }
#Array of hash
customers = [
{ id: 1000, name: 'Clark and Son' },
{ id: 1001, name: 'Clean Fast Co' },
{ id: 1002, name: 'Import International' }
]
#Struct
Person = Struct.new(:name, :age)
person1 = Person.new 'mike', 50
person2 = Person.new 'john', 35
#Set to 'Default title' only if nil or false
title = custom_title || 'Default title'
# Assign if null
search ||= params[:search]
#Safe navigation operator &. (skip if nil)
name = customer&.first_name
print a string to the screen
#print with line break
puts 'This string will print on screen'
#print with no line break
print 'The string will print with no line break'
#print var content (debug)
puts customers.inspect
string methods
# String interpolation
name = 'Mike'
message = "Hello #{name}" # Hello Mike
# get string number of characters
'This is a string'.length # 16
#check if the string is empty
'Hello World'.empty? # false
''.empty? # true
#convert all characters to uppercase
'hello world'.upcase # HELLO WORLD
#convert all characters to lowercase
'HI'.downcase # hi
#convert first characters to uppercase and the rest to lowercase
'mikE'.capitalize # Mike
#remove white space
' This is a string with space '.strip
#return a string left justified and padded with a character
'hello'.ljust(20, '.') # 'hello...............'
#check if a string include character(s)
'hello World'.include? 'World' # true
#chaining 2 or more methods
'Hello World'.downcase.include? 'world' # true
#index position (start at postion 0)
'Welcome to this web site'.index('this') # 11
#return string character(s) (start at position 0)
'This is a string'[1] # h
'This is a string'[0..3] # This
'This is a string'[-1] # g (last character)
#replace first sub string
'Hello dog my dog'.sub 'dog', 'cat'. # Hello cat my dog
#replace all sub string
'Hello dog my dog'.gsub 'dog', 'cat'. # Hello cat my cat
#split a string into an array
'Apple Orange Banana'.split ' ' #['Apple', 'Orange', 'Banana']
# get console keyboard input
input = gets
# get input and chomp last char (ex. new line)
input = gets.chomp
# get command-line arguments (ex. ruby main.rb arg1 arg2)
puts ARGV # ['arg1', 'arg2']
ARGV.each { |option| puts option }
Numbers
number.round 2.68 # 3
number.floor 2.68 # 2
number.ceil 2.68 # 3
2.next # 3
puts 3 / 2 # 1 (integers with integer result integer)
puts 3 / 2.0 # 1.5 (float with integer result float)
puts 2.even? # true
puts 2.odd? # false
# Random number
random_number = rand(1..100)
Loop
loop do
puts "Stop loop by using 'break' statement"
puts "Skip one occurence by using 'next' statement"
end
while number < 100
puts number
number += 1
end
# Range
(1..10).each { |i| puts i }
(1..10).each do |i|
puts i
end
10.times { puts "Hello World" }
Conditionals statement
# Equal == And && Or || Not !
if action == 1
puts "action 1"
elsif action < 5
puts "action not 1 but less than 5"
else
puts "action greater than 5"
end
#Unless (negated if)
puts 'The user is not active' unless active == true
#Ternary operator
active ? 'The user is active' : 'The user is not active'
#Truthy or falsy
# false and nil equates to false.
# Every other object like 1, 0, "" are all evaluated to true
# case when else
case points
when 0
"Not good"
when 1..50
"Better but not great"
when 51..70
"Thats good!"
when 71..99
"Great"
when 100
"Perfect"
else
"Score error"
Array access
fruits = ['Apple', 'Orange', 'Banana']
fruits = %w(Apple Orange Banana)
fruits.length # 3
fruits.first # Apple
fruits.last # Banana
fruits[0] # Apple
fruits[-2] # Orange
fruits[3] # nil
fruits[1..2] # ['Orange', 'Banana']
# iteration
fruits.each do { |fruit| puts fruit }
fruits.each_with_index do |fruit, index|
puts fruit # Apple
puts index # 0
end
Array Methods
fruits.include? 'Orange' # true
[1, 5, 2, 4, 3].sort # [1, 2, 3, 4, 5]
[1, 2, 3].reverse # [3, 2, 1]
fruits.push 'Strawberry' # append at the end
fruits << 'Raspberry' # append at the end
fruits.unshift 'Strawberry' # Append in front
fruits.pop # remove last
fruits.delete_at(0) # remove first element
fruits.shift # remove the first element
fruits.join ', ' # 'apple, orange, banana'
# Add in a new array
array1 = %w(dog cat bird)
array2 = %w(fish hamster)
array3 = array1 + array2 #['dog', 'cat', 'bird', 'fish', 'hamster']
# Concat in the same array
array1.concat array2
puts array1 #['dog', 'cat', 'bird', 'fish', 'hamster']
# Constructing arrays with * splat operator
puts ['dog', *array2, 'bird'] #['dog', 'fish', 'hamster', bird']
Convert between type
123.to_s # convert number to string "123"
"123".to_i # convert string to integer 123
"123".to_f # convert string to float 123.0
#convert to array
(1..10).to_a # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
('a'..'e').to_a # ['a', 'b', 'c', 'd', 'e']
Hash
product = {}
product['title'] = "Mac Book Pro"
product[:price] = 1599.99
product = { 'title' => 'Mac Book Pro', 'price' => 1599.99 }
product = { title: 'Mac Book Pro', price: 1599.99 }
puts product.fetch(:cost, 0) # return default value 0
product.keys # [:title, :price]
product.values # ['Mac Book Pro', 1599.99]
product.each do |key, value|
puts key
puts value
end
Date and time
Time.now.utc # 2020-12-13 03:17:05 UTC
Time.now.to_i # Timestamp 1607829496
christmas = Time.new(2020, 12, 25) #
puts christmas.wday # return 5 (Thursday)
now = Time.now # current time: 2020-12-13 03:08:15 +0000
now.year # 2020
now.month # 12
now.day # 13
now.hour # 3
now.min # 8
now.sec # 15
now.sunday? # true
past = Time.now - 20 # return current time minus 20 seconds
past_day = Time.now - 86400 # 60 secs * 60 mins * 24 hours
past_day = Time.now - 1.day # work only in Rail
#Format Time
# %d Day of the month (01..31)
# %m Month of the year (01..12) Use %-m for (1..12)
# %k Hour (0..23)
# %M Minutes
# %S Seconds (00..60)
# %I Hour (1..12)
# %p AM/PM
# %Y Year
# %A Day of the week (name)
# %B Month (name)
time = Time.new
time.strftime("%d of %B, %Y") # "25 of December, 2020"
Regular Expression (editor: www.rubular.com)
zip_code = /\d{5}/
"Hello".match zip_code # nil
"White House zip: 20500".match zip_code # 20500
"White House: 20500 and Air Force: 20330".scan zip_code # ['20500', '20330']
"Apple Orange Banana".split(/\s+/) # ['Apple','Orange', 'Banana']
Functions
def greeting(name = 'John') # = default argument value
"Hello #{name}" # implicit return
end
puts greeting('Paul') # Hello Paul
# variable number of arguments
def greeting(*names)
names.each { |name| puts name }
end
#naming parameters
def display_product(price, options = {})
puts price, options[:hidden], options[:rounded]
end
display_product 1599, hidden: false, rounded: true
Map, Select, Detect, Reduce and Count
#map (return a modified array)
names = ['paul', 'john', 'peter']
names_capitalize = names.map do |name|
name.capitalize
end
# ['Paul', 'John', 'Peter']
# short hand version
names_capitalize = names.map { |name| name.capitalize }
# Symbol to proc
names_capitalize = names.map &:capitalize
#select (return all match)
products = [
{ name: 'Mac Book Pro', active: true, price: 1599.99 },
{ name: 'iWatch', active: false, price: 599.99 },
{ name: 'iPad Pro', active: true, price: 699.99 },
]
active_products = products.select { | product | product[:active] }
#Detect (return first match)
first_active_product = products.detect { | product | product[:active] }
# Reduce (return one)
total = products.reduce(0) do |total, product|
total = total + product[:price]
end
puts total # 2899.97
# Count (return array count)
nb_products = products.count { |product| product.price > 1000 }
puts nb_products # 1
Module
# Static module method
module Display
def self.hello
puts 'Hello'
end
end
Display.hello
# Class Mix in
module Display
def hello
puts 'Hello'
end
end
require_relative 'display.rb'
class Customer
include Display
end
Customer.new.hello
# Module as namespace
module Person
class Customer
def initialize(name)
@name = name
end
end
end
customer = Person::Customer.new('Mike Taylor')
# Constant
module Contact
ACCESS_KEY = 'abc123'
class Person
ACCESS_KEY = '123abc'
end
end
puts Contact::ACCESS_KEY
puts Contact::Person::ACCESS_KEY
#Module or class private method
module Display
...
def initialize
greeting
end
private
def greeting
puts 'hello'
end
end
OOP
# class declaration
class Product
end
# object instantiation
product = Product.new
# class declaration with constructor and instance variables
class Product
def initialize(name, price, active)
@name = name
@price = price
@active = active
end
end
product = Product.new 'Mac Book Pro', 1599, true
# Getter and Setter
class Product
# set
def price=(value)
@price = value
end
# get
def price
@price
end
end
# attribute accessor (shorthand get & set)
class Product
attr_accessor :name, :price # read and write
attr_reader :name # read only
attr_writer :price # write only
...
end
...
puts product.price # 1599
# instance method
class Product
...
def price_with_tax
# reference to @price directly is not recommended
self.price + (self.price * tax_percent / 100)
# self keyword is optional
end
end
...
puts product.price_with_tax # 1838.85
# private method
class Product
...
private
def profit
...
end
end
...
puts product.profit # NOT ALLOWED
#static class method and static class variable (use self keyword)
def self.calc_tax(amount)
@@count = 1
end
puts Product::calc_tax(1599.99)
# Constant
class Product
MIN_PRICE = 100
def price=(price)
if price < MIN_PRICE
@price = MIN_PRICE
else
@price = price
end
end
end
# Inheritance
class Customer < Person
attr_accessor :number
def initialize(name, number)
# super call the parent same method name
# when call without parentheses then all arguments are pass
# if call with empty arguments () then no arguments pass
super(name)
@number = number
end
def price=(price)
# super call the parent price method
super(price)
@price += 100
end
end
File I/O
# Read
text = File.read('exemple.txt')
# Read by lines
lines = File.readlines("exemple.txt")
lines.each do |line|
puts "Line: #{line}"
end
# Write
File.write('exemple.txt', 'text to write...')
File.open(“index.html”, “w”) do | file |
file.puts ‘text to write’
end
#read csv
require 'csv'
table = CSV.parse(File.read("products.csv"), headers: true)
table[0]["id"] # 1000
table[0]["name"] # "Mac Book Pro"
#write csv
products = [
{ name: "Mac Book Pro", price: 1599 },
{ name: "IPad Pro", price: 799 }
]
CSV.open("products.csv", "w", headers: products.first.keys) do |csv|
products.each { |product| csv << product.values }
end
Errors/Exceptions Handling
# Raise exception and output error message
raise "This is an exception"
# Debut variable value
raise products.inspect # [{:id=>10, :name=>"ipad pro"},{:id=>20, :name=>"Mac book pro"}]
# Exception handling
begin
# Any exceptions here ex. 0 / 1
0 / 1
rescue
# ...will make this code to run
puts "Exception"
do_something()
end
# Exception object
begin
0 / 1
rescue ZeroDivisionError => e
puts e.class.name
puts e.message
end
Latest comments (9)
Thank you for this summary! I'm brushing up my Ruby skills and this cheat sheet jogged a lot of things for me.
For the exception handling part, I think you meant 1 / 0 for ZeroDivisionError. It's written as 0 / 1 in two lines and one comment, which is just 0 and shouldn't produce an error.
Thanks for putting this out there.
I have one suggestion:
Consider making "dealing with Nil values" its own section. :)
Thank you so much for this
This article is very great, thanks
Oh wow!! I love this. I’m going to read it in depth tomorrow to my morning coffee!
Updated the cheat cheat with couples more info related to array contact and couples other things.
Have added it to my snippets :D
This is truly helpfull. Also want to have the same for PHP and Python
This is great!