Introduction to Ruby

'Hello, world!'          # string literal
375                      # integer literal
3.141528                 # float literal
true                     # boolean literal
{ 'a' => 1, 'b' => 2 }   # hash literal
[ 1, 2, 3 ]              # array literal
:sym                     # symbol literal
nil                      # nil literal

irb(main):001:0> 13.to_f
=> 13.0
irb(main):002:0> 13.to_f
=> 13.0
irb(main):003:0> 13.to_s
=> "13"
irb(main):004:0> 

irb(main):013:0> #String interpolation
=> nil
irb(main):014:0> name= "vinay"
=> "vinay"
irb(main):015:0> puts "hello, #{name}"
hello, vinay
=> nil                                                 

irb(main):016:0> "Vinay".capitalize
=> "Vinay"
irb(main):017:0> "vinay".capitalize
=> "Vinay"
irb(main):018:0> "hello".empty?
=> false
irb(main):019:0> "vinay".length
=> 5
irb(main):020:0> "hello world".split
=> ["hello", "world"]
irb(main):021:0> "hello world".split("")
=> ["h", "e", "l", "l", "o", " ", "w", "o", "r", "l", "d"]

irb(main):022:0> #Basic data strctures arrays and hashes
=> nil
irb(main):023:0> [1,4,5,67,8]
=> [1, 4, 5, 67, 8]
irb(main):024:0> #hashes
=> nil
irb(main):025:0> {:dog => "barks"}
=> {:dog=>"barks"}
irb(main):026:0> 

irb(main):021:0> "a string".object_id
=> 237820 irb(main):022:0> "a string".object_id
=> 239900
irb(main):023:0> "a string".object_id
=> 241980
irb(main):024:0> :a_symbol.object_id
=> 2332828
irb(main):025:0> :a_symbol.object_id
=> 2332828
irb(main):026:0> :a_symbol.object_id
=> 2332828

age=20

desired_location= "Bengaluru"
referenced_location= desired_location

reference_location.upcase!

irb(main):034:0> name = gets
Bob
=> "Bob\n"                                  
irb(main):035:0> name = gets.chomp
Bob
=> "Bob"                                                                         
irb(main):036:0> "hello "+ name
=> "hello Bob"
irb(main):037:0> 

name="Vinay Keshava"
def print_full_name(first_name,last_name)
  name = first_name+ ' ' + last_name
  puts name
end

print_full_name 'Mahesh', 'Kumar'
print_full_name 'Suresh', 'Kumar'
puts name

total=0
[1,2,4].each { |number| total += number}
puts total

a=5
3.times do |n|
  a=3
end
puts a

MY_CONSTANT = 'I am available throughout your app.'

$var = 'I am also available throughout your app.'

@@instances = 0

@var = "I'm available throughout the current instance of this class"

var = 'Hello world'

irb(main):001:0> puts "hello world"
hello world
=> nil                                           
irb(main):002:0> print "hello world"
hello world=> nil
irb(main):003:0> gets
hello world
=> "hello world\n"                               
irb(main):004:0> gets.chomp
hello world
=> "hello world"                                                          
irb(main):005:0> name =gets.chomp
hell world
=> "hell world"                                                               
irb(main):006:0> name
=> "hell world"

if true==false
  print "This is not printing"
elsif true== true
  print "True is true hence false is false\n"
end

if 1<2 && 5<6
  print "This is printing because 1 is smaller than 2\n"
end

#case statements
grade = 'F'
pass_fail = case grade
            when 'A' then "Hell yeah distinction"
            when 'B' then "Ahh first class yes yes"
            else "You shall not pass in life"
end
puts pass_fail


percentage = 50.00
pass_fail_percentage = case percentage
                       when 70.00
                         puts "Above 70.00 you dumbshit"
                         total=percentage*100
                       when 80.00
                         puts "80.00 ahh yes yes"
                         total=percentage*100
                        else
                          puts "You shall not pass go graze donkeysss man"
                        end

# unless statements - unless statement works in the opposite way to if statement,it only processes the code if it evaluates to false,unless can be added with else too.
age = 19
unless age <18
  puts "get a job"
else 
  puts " Careful now"
end

# Ternary Operator
response = age < 18? "You still have time to become 19": "You're a grown up kid"
puts response

i=0
#this type of ruby's loop is infinite until you stop it.
loop do
  puts "i is #{i}"
  i+=1
  break if i==10
end

#while loop
i=0
puts "while loop"
while i<10 do
  puts "i is #{i}"
  i+=1
end

#using while loop with gets
while gets.chomp !="yes" do
  puts "Are we there yet?"
end

#until loop
i=0
until i>=10 do
  puts "i is #{i}"
  i +=1
end

# forloops
for i in 0..5
  puts "#{i} zombie coming"
end

#times loop
5.times do
  puts "hello world"
end

#upto and downto loops
5.upto(10) { |num| print "#{num}" }
puts " "
10.downto(5) { |num| print "#{num}" }

#iterators
names = ["vinay","keshava","hello","world"]
names.each { |name| puts name }

##block
names = ["vinay","keshava","hello","world"]
names.each { |name| puts name }

names.each do |name|
  puts "#{name}"
end

num_array=[1,3,4,5,76]
str_array = ["vinay","hello","world","keshava"]

#Creating an array using .new
Array.new
Array.new(3) #creates a new array with size 3
a1 = Array.new(4,7) #creates a new array with size 3,with all the values in these indexes is "7"
puts a1
Array.new(4,true)


#first and last array methods - to access the first and last value of the array.
puts str_array.first
puts str_array.last
puts str_array.first(3)

# adding a element to the array.
num_array=[1,2]
print num_array
puts ""

num_array.push(3,4)
print num_array
puts ""
num_array << 5 # shovel operator which adds 5 to the array.
print num_array

# deleting an element from the array.
num_array.pop     # delete 5
puts num_array

#shift unshift and push and pop
=> [1, 1, 3, 4, 5]
irb(main):005:0> num_array
=> [1, 1, 3, 4, 5]
irb(main):006:0> num_array.shift
=> 1
irb(main):007:0> num_array
=> [1, 3, 4, 5]
irb(main):008:0> num_array.push(10)
=> [1, 3, 4, 5, 10]
irb(main):010:0> num_array.unshift
=> [1, 3, 4, 5, 10]
irb(main):011:0> num_array.unshift(1)
=> [1, 1, 3, 4, 5, 10]
irb(main):012:0> num_array.shift
=> 1
irb(main):013:0> num_array
=> [1, 3, 4, 5, 10]
irb(main):014:0> num_array.shift
=> 1
irb(main):015:0> num_array
=> [3, 4, 5, 10]
irb(main):016:0> num_array.shift
=> 3
irb(main):017:0> num_array
=> [4, 5, 10]
irb(main):018:0> 

irb(main):004:0> hash_with_different_types = { "name"=> "vinay", "degrees"=>["MBA","MTECH","MS"],12=>"twelve" }
=> {"name"=>"vinay", "degrees"=>["MBA", "MTECH", "MS"], 12=>"twelve"}
irb(main):005:0> #creating a hash with Hash.new
=> nil
irb(main):006:0> new_hash=Hash.new
=> {}
irb(main):007:0> new_hash[10=>"ten"]
=> nil
irb(main):008:0> new_hash
=> {}
irb(main):009:0> new_hash={10=>"ten"}
=> {10=>"ten"}
irb(main):010:0> #accessing hash values
=> nil
irb(main):011:0> new_hash[10]
=> "ten"
irb(main):012:0> new_hash.fetch(10)
=> "ten"
irb(main):013:0> #adding and changing data
=> nil
irb(main):014:0> my_hash_example[8]="eighttttee"
=> "eighttttee"
irb(main):015:0> my_hash_example
=> {10=>"ten", 8=>"eighttttee", 7=>"seven"}
irb(main):016:0> my_hash_example[9]="ninie"
=> "ninie"
irb(main):017:0> my_hash_example
=> {10=>"ten", 8=>"eighttttee", 7=>"seven", 9=>"ninie"}
irb(main):018:0> #deleting a hash data element
=> nil
irb(main):019:0> my_hash_example.delete(10)
=> "ten"
irb(main):020:0> my_hash_example
=> {8=>"eighttttee", 7=>"seven", 9=>"ninie"}

irb(main):021:0> #methods in hashes
=> nil
irb(main):022:0> my_hash_example.keys
=> [8, 7, 9]
irb(main):024:0> my_hash_example.values
=> ["eighttttee", "seven", "ninie"]

irb(main):027:0> #merging two hashes
=> nil
irb(main):028:0> my_hash_example.merge(hash_with_different_types)
=> {8=>"eighttttee", 7=>"seven", 9=>"ninie", "name"=>"vinay", "degrees"=>["MBA", "MTECH", "MS"], 12=>"twelve"}
irb(main):029:0> new_merged_hash=my_hash_example.merge(hash_with_different_types)
=> {8=>"eighttttee", 7=>"seven", 9=>"ninie", "name"=>"vinay", "degrees"=>["MBA", "MTECH", "MS"], 12=>"twelve"}
irb(main):030:0> new_merged_hash
=> {8=>"eighttttee", 7=>"seven", 9=>"ninie", "name"=>"vinay", "degrees"=>["MBA", "MTECH", "MS"], 12=>"twelve"}
irb(main):031:0> 

irb(main):031:0> #symbols as hashes
=> nil
irb(main):032:1* american_cars = {
irb(main):033:1*   :chevrolet => "Corvette",
irb(main):034:1*   :fort => "Mustang",
irb(main):035:1*   :ferrari => "1"
irb(main):036:0> }
=> {:chevrolet=>"Corvette", :fort=>"Mustang", :ferrari=>"1"}
irb(main):037:0> american_cars
=> {:chevrolet=>"Corvette", :fort=>"Mustang", :ferrari=>"1"}
irb(main):038:1* japnese_cars = {
irb(main):039:1*   honda: "Accord",
irb(main):040:1*   toyota: "Corolla",
irb(main):041:1*   nissan: "Altime"
irb(main):042:0> }
=> {:honda=>"Accord", :toyota=>"Corolla", :nissan=>"Altime"}

def hello_world_method
  puts "hello world"
end
hello_world_method

def add_two_numbers(a,b)
  puts a+b
  #puts a-b Error: Undefined method
end
add_two_numbers(10,20)
add_two_numbers("hello","world")


#method with return type and argument
def hello_world_with_argument(name)
  return name+" Hello World"
end
puts hello_world_with_argument("vinay")


#default parameters
def method_with_default_parameters(name="Vinay")
  "Hello" + name
end
puts method_with_default_parameters
puts method_with_default_parameters("Mahesh")


#predicate methods- which return a boolean
puts 5.even?
puts 6.even?

puts "Remove all duplicates"
array1 = [1,1,1,1,2]
print array1.uniq

puts "\nRemoving All Nil Elements"
array1=[1,2,4,5,nil,"John"]
array2=array1.compact
#compact removes all the nil elements.
print array1.to_s
print array2.to_s

puts "Remove Odd numbers"
array=[10,34,44,32,21,9,3,8]
even_array= array.reject do |item|
  item.odd?
end
puts even_array


puts "Joining Arrays"
#using concat
numbers1= [1,2,4,5]
numbers2= [5,6]

all_numbers = numbers1+ numbers2
print all_numbers

# Destructuring Array.- Instead of manually assigning values using indexes, we can use this option of destructuring arrays.
puts "\nDestructuring Array"
destructuring_array = [89,90,"Hello","world"]
mark1,mark2,string1,string2 = destructuring_array
puts mark1
puts mark2
puts string2

# Destructuring using greedy variables- adding a star before a variable name makes the variable greedy and that takes all the remaining values
mark1,*other_values= destructuring_array
puts "Destructuring array using greedy variable"
puts mark1
print other_values

puts "\nVariables are greedy,but ruby is damn smart"
mark1, *other_variables, string2= destructuring_array
puts mark1
print other_variables
print string2

puts "\n Creating an array using %w"
w_array = %w{one two three four}
print w_array

puts "\n Quicker way to create array of strings"
array_of_strings= %w[hello world blue green red yellow]
print array_of_strings

puts "\n Quicker way to create array of symbols using %i"
array_of_symbols = %i[symbol1 symbol2 symbol3]
print array_of_symbols

# single line comments
 =begin
 hello world this is a multi line comment in ruby
 =end

> ruby advanced_arrays.rb
Remove all duplicates
[1, 2]
Removing All Nil Elements
[1, 2, 4, 5, nil, "John"][1, 2, 4, 5, "John"]Remove Odd numbers
10
34
44
32
8
Joining Arrays
[1, 2, 4, 5, 5, 6]
Destructuring Array

From: /home/vinay/Documents/learn/ruby/ruby-exercises/advanced_arrays/advanced_arrays.rb:34 :

    29: # Destructuring Array.- Instead of manually assigning values using indexes, we can use this option of destructuring arrays.
    30: puts "\nDestructuring Array"
    31: destructuring_array = [89,90,"Hello","world"]
    32: mark1,mark2,string1,string2 = destructuring_array
    33: binding.pry
 => 34: puts mark1
    35: puts mark2
    36: puts string2
    37: 
    38: # Destructuring using greedy variables- adding a star before a variable name makes the variable greedy and that takes all the remaining values
    39: mark1,*other_values= destructuring_array

[1] pry(main)> mark1
=> 89
[2] pry(main)> mark2
=> 90
[3] pry(main)> string1
=> "Hello"
[4] pry(main)> 

puts "Select enumerable methods"
friends = ['Sharon','Vinay','Suresh','Mahesh']
print friends.select { |friend| friend!= 'Vinay'}


puts "\n\nEach enumerable methods"
friends.each { |friend| puts "hello"+ friend}

puts "each_with_index method- returns two block elements,the value and the index of the value"
friends.each_with_index { |fruit, index| print fruit if index.even? }

puts "\n the map method,instead of creating two separate arrays or creating a new array to put the same data,we can use the  map"
friends.each { |friend| friend.upcase }
# the above just converts but doesn't saves to the original array,instead creating a new array will be like duplicating data
friends.map { |friend| friend.upcase}
print friends


puts "\nreduce method- takes an array or hash and reduces it to single object"
my_numbers = [10,20,40,90]
print my_numbers.reduce { |sum, number| sum+number }

puts "\n Bang methods end with an exclamation and often modify the object they are called on"
#just like friends in the above example if we want to modify the original object we use bang method,we use the above map method to modify the original array
friends.map! { |friend| friend.upcase }
print friends

puts "\n Return values of enumerables - it is not a good practice to use bang methods and modify original objects,instead return the enumerables and assign it to a new object"
invited_friends = friends.select { |friend| friend!='VINAY' }
print invited_friends

#include? predicate enumerable method
numbers = [5,7,7,8]
print numbers.include?(8)

#any method returns true if any elements in array or hash matches the condition within the block;otherwise return false
print numbers.any? { |num| num>10 }
print numbers.any? { |num| num<10 }

#all? method returns true if all the elements in your array or hash matches the condition
puts "\nall? predicate enumerable method"
print numbers.all? {|num| num>1}
# none? method returns true only if the condition in the block matches with none of the elements in array/hash,otherwise it returns false.
print numbers.none? { |num| num>20}
#saying there are no numbers greater than 20