1.next # 2

# single line comment

=begin
multiline
comment
=end

=begin Comment line 1 =end

puts "Hello world!"  # Inline comment about the code

# Addition
1 + 1   #=> 2

# Subtraction
2 - 1   #=> 1

# Multiplication
2 * 2   #=> 4

# Division
10 / 5  #=> 2
17 / 5    #=> 3, not 3.4
17 / 5.0  #=> 3.4

# Exponent
2 ** 2  #=> 4
3 ** 4  #=> 81

# Modulus (find the remainder of division)
8 % 2   #=> 0  (8 / 2 = 4; no remainder)
10 % 4  #=> 2  (10 / 4 = 2 with a remainder of 2)

a = 10
b = 20

a == b #=> false
a != b #=> true
a > b #=> false
a < b #=> true
a >= b #=> false
a <= b #=> true

# Comparison Operator
a <=> b #=> -1
c = 20
c <=> b #=> 0
c <=> a  #=> 1

# Used to test equality within a when clause of a case statement.
(1...10) === 5 #=> true

# True if the receiver and argument have both the same type and equal values.
1.eql?(1.0) #=> false

c = a + b  #=> 30
c += a #=> 40
c -= a #=> 30
c *= a #=> 300
c /= a #=> 30
c %= a #=> 3
c **= a #=> 59049

# Ruby Parallel Assignment

a = 10
b = 20
c = 30

a, b, c = 10, 20, 30

# Ruby Bitwise Operators

a = 60
b = 13
# & Binary AND Operator copies a bit to the result if it exists in both operands.

a & b #=> 12

# | Binary OR Operator copies a bit if it exists in either operand.

a | b #=> 61

# ^ Binary XOR Operator copies the bit if it is set in one operand but not both.

a ^ b #=> 49

# ~ Binary Ones Complement Operator is unary and has the effect of 'flipping' bits.

~a

# << Binary Left Shift Operator. The left operands value is moved
# left by the number of bits specified by the right operand.

a << 2

# >> Binary Right Shift Operator. The left operands value is moved
# right by the number of bits specified by the right operand.

a >> 2


# Ruby Logical Operators

a and b #=> true.
a or b #=> true.
a && b #=> true.
(a || b) #=> true.
!(a && b) #=> false.
not(a && b) #=> false.

# Ruby Ternary Operator

# ? :
# If Condition is true ? Then value X : Otherwise value Y
a == 10 ? puts 'Right' : puts 'Wrong'

# Ruby Range Operators

# .. Creates a range from start point to end point inclusive.
1..10 #=> Creates a range from 1 to 10 inclusive.

# ... Creates a range from start point to end point exclusive.
1...10 #=> Creates a range from 1 to 10 exclusive.

current_weather = "rainy"
_weather = "sunny"

@current_weather = "rainy"

@current_weather = "rainy"

$current_weather = "rainy"

WEATHER = "rainy".freeze

defined? count
"local-variable"
defined? @id
"instance-variable"
defined? @@name
"class variable"
defined? $version
"global-variable"
defined? PI
"constant"

num = 2
puts 'two' if num == 2

temp = 19

if temp >= 25
  puts "hot"
elsif temp < 25 && temp >= 18
  puts "normal"
else
  puts "cold"
end

# output
# normal

# The unless is opposite of if, evaluates when the statement is false

name = "rob"

# if name != "bob"
unless name == "bob"
  puts "hello stranger"
else
  puts "hello bob"
end
# output
# hello stranger

num = 6
puts 'not two' unless num == 2
# output
# not two

# case returns the value of the last expression executed

case input
# check an integer, 19
when 19
  puts "It's 19"
  # check a float number, 33.3
when 33.3
  puts "It's 33.3"
  # check an exact string, "Zaman"
when "Zaman"
  puts "Hi Zaman"
when 10
  puts "It's 10"
  # check against a range
when 7..11
  puts "It's between 7 and 11"
  # check against multiple values, "coffee"
when "tea", "coffee"
  puts "Happy days"
  # check against a regular expression, "aA6"
when /^a[A-Z]+[0-6]+$/
  puts "It's a valid match"
  # check any string by comparing against the String class, "any string"
when String
  puts "It's a String"
end

# using short syntax
case input
  when 19 then puts "It's 19"
end

# optional fallthrough
case input
  when 19 then puts "It's 19"
else
  puts "It's not 19"
end

# get the return value
marks = 86

result = case marks
         when 0..49 then "Fail"
         when 50..64 then "Pass"
         when 65..74 then "Credit"
         when 75..84 then "Distinction"
         when 85..100 then "High Distinction"
         else "Invalid marks"
         end

puts result
# High Distinction

# both are synonymous
a = 37
a.kind_of? Integer
# true
a.is_a? Integer
# true

week_days = {sunday: 11, monday: 222}

name = "World"
puts "Hello #{name}"

puts "The total is #{1+1}"
# "the total is 2"

string = "abc123"
string[0,3]
# "abc"

string[3,3]
# "123"

string[0..-2]
# "abc12"

#remove or replace the substring
string[0..2] = ""
puts string
# "123"

2.even?
# true
3.even?
# false
65.chr
#=> "A"
36.gcdlcm(60)
#=> [12, 180]
36.lcm(60)
#=> 180
(-12345).abs
#=> 12345
1.next
#=> 2
(-1).succ
#=> 0
1.pred
#=> 0
5.remainder(3)
#=> 2
12345.to_s
#=> "12345"
12345.to_s(2)
#=> "11000000111001"
12345.to_s(8)
#=> "30071"
12345.to_s(10)
#=> "12345"
12345.to_s(16)
#=> "3039"
12345.to_s(36)
#=> "9ix"
12345.digits
#=> [5, 4, 3, 2, 1]

# .. for creating inclusive ranges

range = 1..10
range.to_a
# output
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

# ... for creating exclusive ranges

range = 1...10
range.to_a
# output
# [1, 2, 3, 4, 5, 6, 7, 8, 9]

(1..20).step(2) { |number| puts "#{number}"}
# output
# 1
# 3
# 5
# 7
# 9
# 11
# 13
# 15
# 17
# 19

def method_name(parameter1, parameter2)
    puts "#{parameter1} #{parameter2}"
    parameter1 + parameter2
end

res = method_name(20, 10)
# output
# 30

def method_name(parameter1, parameter2)
    puts "#{parameter1} #{parameter2}"
    return parameter1 + parameter2
end
# output
# 30

res = method_name(parameter1, parameter2)
# In Ruby you can call methods without parentheses
res = method_name parameter1, parameter2

def method_name(parameter1, parameter2, type = "ADD")
  puts "#{parameter1} #{parameter2}"
  return parameter1 + parameter2 if type == "ADD"
  return parameter1 - parameter2 if type == "SUB"
end

res = method_name(20, 10)
# output
# 30

def method_name(num1, num2 = num1)
  return num1 + num2
end

res = method_name(10)
# output
# 20

def method_name(type, *values)
  return values.reduce(:+) if type == "ADD"
  return values.reduce(:-) if type == "SUB"
end

numbers = [2, 2, 2, 3, 3, 3]

res = method_name("ADD", *numbers)
# output
# 15

res = method_name("SUB", *numbers)
# output
# -11

# or you can provide the values like this
res = method_name("ADD", 2, 2, 2, 3, 3, 3)
# output
# 15

"some text".nil?
# false
nil.nil?
# true

def is_vowel?(char)
  ['a','e','i','o','u'].include? char
end

is_vowel? 'a'
# true
is_vowel? 'b'
# false

class Mobile
  def self.ring
    "ring ring ring..."
  end
end

Mobile.ring

class Mobile
  def Mobile.ring
    "ring ring ring..."
  end
end

Mobile.ring

class Mobile
  class << self
    def ring
      "ring ring ring..."
    end
  end
end

Mobile.ring

Mobile = Class.new do
  def self.ring
    "ring ring ring..."
  end
end

Mobile.ring

Mobile = Class.new

class << Mobile
  def ring
      "ring ring ring..."
  end
end

Mobile.ring

# return value
def give_me_data
  data = yield
  puts "data = #{data}"
end

give_me_data { "Big data" }

# output
# data = Big data

# single line block
salary = [399, 234, 566, 533, 233]
salary.each { |s| puts s }

# puts s = block body
# |s| = block arugments

# multiline block
salary.each do |s|
  a = 10
  res = a * s
  puts res
end

# block body
# a = 10
# res = a * s
# puts res

# block arugments
# |s|

# passing a block implicitly
def give_me_data
  puts "I am inside give_me_data method"
  yield
  puts "I am back in give_me_data method"
end

give_me_data { puts "Big data" }

# output
# I am inside give_me_data method
# Big data
# I am back in give_me_data method

# call multiple times
def give_me_data
  yield
  yield
  yield
end

give_me_data { puts "Big data" }

# output
# Big data
# Big data
# Big data

# call with block arguments

def give_me_data
  yield 10
  yield 100
  yield 30
end

give_me_data { |data| puts "Big data #{data} TB" }

# output
# Big data 10 TB
# Big data 100 TB
# Big data 30 TB

# call with multiple block arguments

def give_me_data
  yield "Big data", 10, "TB"
  yield "Big data", 100, "GB"
  yield "Big data", 30, "MB"
end

give_me_data { |text, data, unit| puts "#{text} #{data} #{unit}" }

# output
# Big data 10 TB
# Big data 100 GB
# Big data 30 MB

#  block will try to return from the current context
give_me_data
  puts "I am inside give_me_data method"
end

def test
  puts "I am inside test method"
  give_me_data { return 10 } # code returns from here
  puts "I am back in test method"
end

return_value = test

# output
# I am inside test method
# I am inside give_me_data method
# 10

# passing a block explicitly by using an ampersand parameter, here we are explicitly defining the method with block parameter and calling it
def give_me_data(&block)
  block.call
  block.call
end

give_me_data { puts "Big data" }

# output
# Big data
# Big data

def give_me_data
  yield
end

give_me_data

# output
# LocalJumpError: no block given (yield)

# you can use block_given? method to handle the exception and make the block optional

def give_me_data
  return "no block" unless block_given?
  yield
end

give_me_data { puts "Big data" }
give_me_data

# output
# Big data

def give_me_data(&block)
  block.call if block
end

give_me_data { puts "Big data" }
give_me_data

# output
# Big data

p = Proc.new { puts "Hello World" }

def give_me_data(proc)
  proc.call
end

give_me_data p

# output
# Hello World

# arbitrary arguments
p = Proc.new { |count| "Hello World " * count }

def give_me_data(proc)
  proc.call 5, 2
end

give_me_data p

# output
# "Hello World Hello World Hello World Hello World Hello World "

#  proc will try to return from the current context
p = Proc.new { return 10 }
p.call

# output
LocalJumpError: unexpected return

# because you can’t return from the top-level context

def give_me_data
  puts "I am inside give_me_data method"
  p = Proc.new { return 10 }
  p.call # code returns from here
  puts "I am back in give_me_data method"
end

return_value = give_me_data
puts return_value

# output
# I am inside give_me_data method
# 10

# there are multiple ways to declare a lambda
l = lambda { puts "Hello World" }
# shorthand
l = -> { puts "Hello World" }

# call the lambda
l.call

# output
# Hello World

# there are multiple ways you can call a lambda
l.()
l[]

# strict arguments
l = -> (count) { "Hello World " * count }
l.call 5

# output
# "Hello World Hello World Hello World Hello World Hello World "

l.call 5, 2

# output
wrong number of arguments (given 2, expected 1)

# lambdas return from the lambda itself, like a regular method
l = -> { return 10 }
l.call

# output
# 10

def give_me_data
  puts "I am inside give_me_data method"
  l = -> { return 10 }
  l.call
  puts "I am back in give_me_data method"
end

return_value = give_me_data
puts return_value

# output
# I am inside give_me_data method
# I am back in give_me_data method
# nil # because puts return nil

array = Array.new   #=> []
# or
array = []

# An Array can contain different types of objects.
array = [1, "two", 3.0] #=> [1, "two", 3.0]

numbers = Array.new(3)            #=> [nil, nil, nil]
numbers = Array.new(3, 7)         #=> [7, 7, 7]
numbers = Array.new(3, true)      #=> [true, true, true]

numbers = []
numbers.fill(7, 0..2)   #=> [7, 7, 7]

array_with_hashes = Array.new(2) { {} } #=> [{}, {}]
array_with_hashes[0][:name] = "Bob"
array_with_hashes[0][:id] = 10          #=> [{:name=>"Bob", :id=>10}, {}]

temperature_data = [
                     ["A908", 38],
                     ["A909", 37],
                     ["A910", 38],
                   ]
temperature_data[0]    #=> ["A908", 38]
temperature_data[0][0] #=> "A908"
temperature_data[0][1] #=> 38

str_array = ["This", "is", "a", "small", "array"]
str_array[0]            #=> "This"
str_array[1]            #=> "is"
str_array[4]            #=> "array"

# A negative index is an offset, backwards, from the end of the array:

# Index -1 indicates the last element.
str_array[-1]             #=> "array"

# Index -2 indicates the next-to-last element.
str_array[-2]             #=> "small"

# A negative index is in range if its absolute value is
# not larger than the size of the array.

str_array[-6]             #=> nil

# str_array.at
puts str_array.at(0)      #=> "This"

arr = [1, 2, 3, 4, 5, 6]
arr[100]                  #=> nil
arr[-3]                   #=> 4
arr[2, 3]                 #=> [3, 4, 5]
arr[1..4]                 #=> [2, 3, 4, 5]
arr[1..-3]                #=> [2, 3, 4]

# To raise an error for indices outside of the array bounds
# or else to provide a default value when that happens, you can use fetch.

arr = ['a', 'b', 'c', 'd', 'e', 'f']
arr.fetch(100)            #=> IndexError: index 100 outside of array bounds: -6...6
arr.fetch(100, "oops")    #=> "oops"


arr = [1, 2, 3, 4, 5, 6]

# The special methods first and last will return the first and last elements of an array
arr.first                #=> 1
arr.last                 #=> 6

# To return the first n elements of an array, use take
arr.take(3)             #=> [1, 2, 3]

# drop does the opposite of take, by returning the elements
# after n elements have been dropped
arr.drop(3)            #=> [4, 5, 6]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.push(11)          #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
numbers.push(12, 13, 14)  #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

num_array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
num_array.pop             #=> 10
num_array                 #=> [1, 2, 3, 4, 5, 6, 7, 8, 9]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.unshift(0)          #=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.unshift(-3, -2, -1) #=> [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

numbers.shift #=> 1
numbers       #=> [2, 3, 4, 5, 6, 7, 8, 9, 10]

numbers.delete_at(2) #=> 4
numbers              #=> [2, 3, 5, 6, 7, 8, 9, 10]

numbers.delete(2) #=> 2
numbers           #=> [3, 5, 6, 7, 8, 9, 10]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.insert(0, 0)           #=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.insert(0, -3, -2, -1)  #=> [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

numbers.insert(-1, 12, 13, 14) #=> [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14]
numbers.insert(-4, 11)         #=> [-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

numbers = Array.new(10) { |n| n = n * 2 } #=> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

numbers = Array(100..110) #=> [100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110]

# or we can convert a range to an array
(100..110).to_a #=> [100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110]

arr = ['foo', 0, nil, 'bar', 7, 'baz', nil]
arr.compact  #=> ['foo', 0, 'bar', 7, 'baz']
arr          #=> ['foo', 0, nil, 'bar', 7, 'baz', nil]
arr.compact! #=> ['foo', 0, 'bar', 7, 'baz']
arr          #=> ['foo', 0, 'bar', 7, 'baz']

arr = [2, 5, 6, 556, 6, 6, 8, 9, 0, 123, 556]
arr.uniq #=> [2, 5, 6, 556, 8, 9, 0, 123]

# when you have single line block
salary = [399, 234, 566, 533, 233]
salary.each { |s| puts s }
# output
# 399
# 234
# 566
# 533
# 233

# when you have a multiline block, you can replace the curly brackets {} with do and end
salary.each do |s|
  a = 10
  res = a * s
  puts res
end
# output
# 3990
# 2340
# 5660
# 5330
# 2330

# or you can do the same thing just using curly brackets {} and semicolons as separators instead of new lines
salary.each { |s| a = 10 ; res = a * s ; puts res }

salary = [399, 234, 566, 533, 233]
salary.each_with_index { |value, index| puts "#{index} #{value}" }
# output
# 0 399
# 1 234
# 2 566
# 3 533
# 4 233

colors = [{color: "red", count: 3}, {color: "red", count: 5}, {color: "black", count: 4}]
colors.each_with_object(Hash.new(0)) { |color, hash| hash["color_"+color[:color]] = color[:color].upcase; hash["count_"+color[:color]] += color[:count] }
# output
{"color_red"=>"RED", "count_red"=>8, "color_black"=>"BLACK", "count_black"=>4}

[1, 2, 3].each_with_object(0) { |number, sum| sum += number}
# output
# 0
# because 0 is immutable, since the initial object is 0, the method returns 0

salary = [399, 234, 566, 533, 233]
salary.each_index { |i| puts i}
# output
# 0
# 1
# 2
# 3
# 4

salary = [399, 234, 566, 533, 233]
salary.map { |s|  s * 10  }
# returns
# [3990, 2340, 5660, 5330, 2330]

# on the other hand each returns the originl values
salary = [399, 234, 566, 533, 233]
salary.each { |s|  s * 10  }
# returns
# [399, 234, 566, 533, 233]

salary = [399, 234, 566, 533, 233]
salary.collect { |s| s > 400 }
# output
# [false, false, true, true, false]

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = 0
while index < planets.size
  puts "#{planets[index]}"
  index += 1
end

a = 1
star = '*'
while a <= 10
  puts star
  star += '*'
  a += 1
end

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = 0
loop do
  puts "#{planets[index]}"
  index += 1
  break if planets[index] == "Mars" or index > planets.size
end

for value in [2, 3, 5, 7]
  puts value
end

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
index = planets.size - 1
until index < 0
  puts "#{planets[index]}"
  index -= 1
end

a = 1
star = '*'
until star.length > 10
  puts star
  star += '*'
  a += 1
end

10.times { puts "#{rand(1..100)}"}
# output
# will print 10 random numbers

# just because you can doesn't mean you should iterate an array like this
data_sample = [2, 3, 5, 7]
data_sample.size.times { |index| puts "#{data_sample[index]}" }
# output
# 2
# 3
# 5
# 7

data_sample = [2, 3, 5, 7]
0.upto((data_sample.size - 1) / 2) { |index| puts "#{data_sample[index]}" }
# output
# 2
# 3

data_sample = [2, 3, 5, 7]
(data_sample.size - 1).downto(data_sample.size / 2) { |index| puts "#{data_sample[index]}" }
# output
# 7
# 5

1.step(20, 2) { |number| puts "#{number}"}
# output
# 1
# 3
# 5
# 7
# 9
# 11
# 13
# 15
# 17
# 19

19.step(1, -2) { |number| puts "#{number}"}
# output
# 19
# 17
# 15
# 13
# 11
# 9
# 7
# 5
# 3
# 1

numbers = [2, 2, 2, 2, 2]
numbers.inject{ |res, n| res + n }
# output is the result of the sum of all numbers
# if you do not set an initial value for res, then the first element of the array is used as the initial value of res
# 10

# now set the value of res with 11
numbers = [2, 2, 2, 2, 2]
numbers.inject(11) { |res, n| res + n }
# so 11 + 2, 13 + 2, 15 + 2, 17 + 2 and 19 + 2
# 21

# using symbol
numbers = [2, 2, 2, 2, 2]
numbers.inject(:+)
# output
# 10

# using initial value and a symbol
numbers = [2, 2, 2, 2, 2]
numbers.inject(11, :+)
# output
# 21

numbers = [2, 2, 2, 2, 2]
numbers.reduce(11, :+)
# output
# 21

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.detect { |name| name.start_with?("E") and name.end_with?("h") }
# output
# Earth

salary = [399, 234, 566, 533, 233]
salary.detect { |s| s > 1000 }
# output
# nil

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.find { |name| name.start_with?("E") and name.end_with?("h") }
# output
# Earth

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.select { |n| n % 2 == 0 }
# now you have an array of even numbers, how cool is that
# [2, 4, 6, 8, 10]
# returns an empty array if there is no value that satisfy your logic
[1, 1, 1].select { |n| n % 2 == 0 }
# no even numbers
# []

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.reject { |n| n % 2 == 0 }
# reject if the number is even, so now we have an array of odd numbers
# [1, 3, 5, 7, 9]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.keep_if { |n| n % 2 == 0 }
# numbers array holds only even numbers
# [2, 4, 6, 8, 10]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.delete_if { |n| n % 2 == 0 }
# numbers array holds only odd numbers
# [1, 3, 5, 7, 9]

numbers = [1, 2, 3, 1, 2, 3, 0]
numbers.drop_while { |n| n < 3 }
# is 3 less than 3, returns false, so drop 1, 2
# [3, 1, 2, 3, 0]

words = %w[first second third fourth fifth sixth]
str = ""
words.reverse_each {|word| str += "#{word} "}
p str #=> "sixth fifth fourth third second first "

[2, 4, 6, 8, 10].all? { |num| num % 2 == 0 }
# true
[1, 4, 6, 8, 10].all? { |num| num % 2 == 0 }
# false

[1, 3, 5, 7, 10].any? { |num| num % 2 == 0 }
# true
[1, 3, 5, 7, 19].any? { |num| num % 2 == 0 }
# false

[1, 3, 2, 5, 7].one? { |num| num % 2 == 0 }
# true
[1, 3, 2, 5, 4].one? { |num| num % 2 == 0 }
# false

[1, 3, 5, 7, 9].none? { |num| num % 2 == 0 }
# true
[2, 3, 5, 7, 9].none? { |num| num % 2 == 0 }
# false

[].empty?
# true
[1, 3, 5, 7, 9].empty?
# false

[0, 1, 2, 3] & [1, 2] # => [1, 2]
[0, 1, 0, 1] & [0, 1] # => [0, 1]

[0, 1, 2, 3].intersection([0, 1, 2], [0, 1, 3]) # => [0, 1]
[0, 0, 1, 1, 2, 3].intersection([0, 1, 2], [0, 1, 3]) # => [0, 1]

a = [0, 1] + [2, 3]
a # => [0, 1, 2, 3]

[0, 1, 1, 2, 1, 1, 3, 1, 1] - [1] # => [0, 2, 3]
[0, 1, 2, 3] - [3, 0] # => [1, 2]
[0, 1, 2] - [4] # => [0, 1, 2]

[0, 1, 2, 3].union([4, 5], [6, 7]) # => [0, 1, 2, 3, 4, 5, 6, 7]
[0, 1, 1].union([2, 1], [3, 1]) # => [0, 1, 2, 3]
[0, 1, 2, 3].union([3, 2], [1, 0]) # => [0, 1, 2, 3]

[0, 1, 1, 2, 1, 1, 3, 1, 1].difference([1]) # => [0, 2, 3]
[0, 1, 2, 3].difference([3, 0], [1, 3]) # => [2]
[0, 1, 2].difference([4]) # => [0, 1, 2]

a = [0, 1, 2]
a1 = [3, 4]
p = a.product(a1)
p.size # => 6 # a.size * a1.size
p # => [[0, 3], [0, 4], [1, 3], [1, 4], [2, 3], [2, 4]]

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.include? "Mars"
# output
# true

planets.include? "Pluto"
# output
# false

# you can either use size or length, both are synonymous
planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.size
# output
# 8

planets.length
# output
# 8

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers.clear
# output
# []

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers[0]
# or
numbers.first
# output
# 1

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
numbers[-1]
# or
numbers.last
# output
# 10

a = ["tom", "mot", "otm"]
b = [2, 3, 5]

a.zip(b)

# outout
# [["tom", 2], ["mot", 3], ["otm", 5]]

primes = [7, 2, 3, 5]
sorted_primes = primes.sort
puts "#{sorted_primes}"
# output
# [2, 3, 5, 7]

primes = [7, 2, 3, 5]
primes.sort!
puts "#{primes}"
# output
# [2, 3, 5, 7]

planets = ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"]
planets.sort
# output
# ["Earth", "Jupiter", "Mars", "Mercury", "Neptune", "Saturn", "Uranus", "Venus"]

planets.sort_by { |p| p }
# output
# ["Earth", "Jupiter", "Mars", "Mercury", "Neptune", "Saturn", "Uranus", "Venus"]

planets.sort_by { |p| p.length }
# output
# ["Mars", "Earth", "Venus", "Saturn", "Uranus", "Neptune", "Jupiter", "Mercury"]

primes = [7, 2, 3, 5]
primes.max_by { |p| p }
# output
# 7

# numbers[start..end], both index are inclusive
puts numbers[0..3]
# 1
# 2
# 3
# 4

# numbers[start..end], end index is exclusive
puts numbers[0...3]
# 1
# 2
# 3

# or numbers[start..length]
puts numbers[0, 1]
# 1

primes = [7, 2, 3, 5]
primes.take(3)
# [7, 2, 3]

primes = [7, 2, 3, 5]
primes.fetch(3)
# 5
# Fetch will throw an error if the element does not exist
primes.fetch(10)
# (index 10 outside of array bounds: -4...4)
# or get an default value
primes.fetch(10, -1)
# -1

primes = [7, 2, 3, 5]
primes.drop(3)
# [5]

primes = [7, 2, 3, 5]
primes.shift
# [2, 3, 5]

primes = [7, 2, 3, 5]
primes.pop
# [7, 2, 3]

primes = [7, 2, 3, 5]
primes.delete_at(-1)
# [7, 2, 3]

primes = [7, 2, 3, 5, 5]
primes.delete(5)
# [7, 2, 3]

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 1]
numbers.uniq
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

students = Hash.new
or
students = {}

puts "#{students[:name]}"
# nil

students = Hash.new
students = { name: 'John', email: '[email protected]' }
puts "#{students[:name]}"
# or
students = Hash.new
students = { :name => 'John', :email => '[email protected]' }
puts "#{students[:name]}"

students = Hash.new("no data")
puts "#{students[:email]}"
# no email
# or
students = Hash.new
students.default = "no data"
puts "#{students[:email]}"
# no email

students = Hash.new("no data")
students[:email] = "[email protected]"
puts "#{students[:email]}"
# [email protected]
puts "#{students[:id]}"
# no data
puts "#{students[:name]}"
# no data
students[:id].upcase!
puts "#{students[:email]}"
# [email protected]
puts "#{students[:id]}"
# NO DATA
puts "#{students[:name]}"
# NO DATA

students = Hash.new {|hash, key| hash[key] = "no data" }
students[:email] = "[email protected]"
puts "#{students[:email]}"
# [email protected]
puts "#{students[:id]}"
# no data
puts "#{students[:name]}"
# no data
students[:id].upcase!
puts "#{students[:email]}"
# [email protected]
puts "#{students[:id]}"
# NO DATA
puts "#{students[:name]}"
# no data

numbers = [1, 1, 1, 2, 4, 65, 55, 54, 55]
freq_hash = numbers.each_with_object(Hash.new(0)) { |number, hash| hash[number] += 1 }
puts "#{freq_hash}"
# output
# {1=>3, 2=>1, 4=>1, 65=>1, 55=>2, 54=>1}

numbers = [1, 1, 1, 2, 4, 65, 55, 54, 55]
freq_hash = Hash.new(0)
numbers.each { |number| freq_hash[number] += 1 }
puts "#{freq_hash}"
# output
# {1=>3, 2=>1, 4=>1, 65=>1, 55=>2, 54=>1}

numbers = [1, 1, 1, 2, 4, 65, 55, 54, 55]
numbers.tally
# output
# {1=>3, 2=>1, 4=>1, 65=>1, 55=>2, 54=>1}

# Hash.new(0) sets a default value of 0 for every key that do not exist in the hash.
# {} or Hash.new() sets nil for every key

h1 = Hash.new(0)
h1[:count] += 1
puts "#{h1[:count]}"
# output
# 1

puts "#{h1[:new_key]}"
# output
# 0

h2 = {}
h2[:count] += 1
# error
"undefined method `+` for nil:NilClass"

hash = {e: 2, d: 3, c: 5, b: 7, a: 11}
hash.sort
# output
# [[:a, 11], [:b, 7], [:c, 5], [:d, 3], [:e, 2]]

hash.sort_by { |k, v| k }
# output
# [[:a, 11], [:b, 7], [:c, 5], [:d, 3], [:e, 2]]

hash.sort_by { |k, v| v }
# output
# [[:e, 2], [:d, 3], [:c, 5], [:b, 7], [:a, 11]]

hash = {e: 2, d: 3, c: 5, b: 7, a: 11}
hash.max_by { |k, v| v }
# output
# [:a, 11]

# Ruby program to illustrate 'while' loop

# variable count
count = 4

# using while loop
# here conditional is count i.e. 4
while count >= 1

  # statements to be executed
  puts "Ruby Cheatsheet"
  count = count - 1

  # while loop ends here
end

# Ruby program to illustrate 'for'
# loop using range as expression

text = "Ruby Cheatsheet"

# using for loop with the range
for count in 1..5 do

  puts text

end

# Ruby program to illustrate 'do..while'loop

# starting of do..while loop
loop do

  puts "Ruby Cheatsheet"

  val = '7'

  # using boolean expressions
  if val == '7'
    break
  end

  # ending of ruby do..while loop
end

var = 7

# using until loop
# here do is optional
until var == 11 do

  # code to be executed
  puts var * 10
  var = var + 1

  # here loop ends
end

# by using break keyword
salary = [399, 234, 566, 533, 233]
salary.each do |s|
  break if s == 566

  puts s
end
#output
# 399
# 234

# by using next keyword
salary = [399, 234, 566, 533, 233]
salary.each do |s|
  next if s == 533

  puts s
end
# output
# 399
# 234
# 566
# 233

data = [456, 3000]
retry_count = 0
status = "network failure"
sum = 0
data.each do |d|
    if retry_count == 3
        status = "connection established"
        retry_count = 0
        redo
    elsif status == "network failure" and retry_count < 5
        puts "network failure #{retry_count}"
        retry_count += 1
        redo
    elsif status == "connection established"
        puts d
        sum += d
    end
end

# output of sum
# 3456

numbers = [2, 2, 44, 44]
sum = 0
begin
    numbers.each do |s|
        if rand(1..10) == 5
            puts "hi 5, let's do it again!"
            sum = 0
            raise "hi 5"
        end
        puts s
        sum += s
    end
rescue
    retry
end

class Person
    # when you create a new object, it looks for a method named initialize and executes it, like a constructor in java
    # def initialize(name, number)
    #    @name = name
    #    @number = number
    # end

    # instance variable
    # @name

    # class variable
    # @@count

    # attr_accessor acts as a getter and setter for the following instance attributes
    attr_accessor :name, :number

    # class variable must be initialized
    @@count = 0

    def self.count
        @@count
    end

    def self.count=(count)
        @@count = count
    end

    def initialize
        @@count += 1
    end
end

# create an instance of the Person class
p1 = Person.new

# set attributes of the Person class
p1.name = "Yukihiro Matsumoto"
p1.number = 9999999999

# get attributes of the Person class
puts "#{p1.name}"
puts "#{p1.number}"
puts "#{Person.count}"

# Yukihiro Matsumoto
# 9999999999
# 1

p2 = Person.new
p2.name = "Yukihiro Matsumoto"
p2.number = 9999999999

# get attributes of the Person class
puts "#{p2.name}"
puts "#{p2.number}"
puts "#{Person.count}"

# Yukihiro Matsumoto
# 9999999999
# 2

# set class variable
Person.count = 3
puts "#{Person.count}"
# 3