select, sort and find

_select-sort-find.md

select, sort and find

Demo code will use the person class from yesterday

class Person
  attr_reader :name, :job_title, :phone, :salary

  @employee_number = 0
  def initialize(name, job_title, phone, salary)
    @name = name
    @job_title = job_title
    @phone = phone
    @salary = salary.to_i
    @number = Person.increase_number
  end

  def self.increase_number
    @employee_number += 1
  end

  def description
    "##{@number} #{@name} is a #{@job_title} and has salary #{@salary}"
  end
end

people = [Person.new('Kerry MacFarlane', 'developer', '555-1234', '60000'),
          Person.new('Terry Grayson', 'manager', '555-3456', '90000'),
          Person.new('Sam Ferguson', 'developer', '555-4321', '65000'),
          Person.new('Jossef Goldberg', 'designer', '555-2222', '65000'),
          Person.new('Doris Hartwig', 'engineer', '555-6767', '75000'),
          Person.new('Steven Selikoff', 'developer', '555-2424', '65000'),
          Person.new('Zheng Mu', 'developer', '555-5885', '65000'),
          Person.new('Greg Komosinski', 'analyst', '555-9090', '55000')
          ]

select

array = Array.new(10) { rand(1...100) }
print array
puts
selected_numbers = array.select do |number|
    number > 50
  end
print selected_numbers
puts

Selecting objects based on instance variable values

selected_people = people.select do |person|
  person.salary > 65_000
end
puts 'selected people'
selected_people.each { |p| puts p.description }

sort

Sort example with numbers

array = Array.new(10) { rand(1...100) }

print array
puts
print array.sort
puts

Sort example with strings

array = ['4', '23', '45', '2', '19']

print array
puts
print array.sort 
puts

Can resolve the string sort issue using a custom sort

array = ['4', '23', '45', '2', '19']

print array
puts
print array.sort { |x, y| x.to_i <=> y.to_i }
puts

Sorting objects

puts 'before sort'

people.each { |p| puts p.description }

sorted_people = people.sort { |x, y| x.name <=> y.name }

puts 'after sort'

sorted_people.each { |p| puts p.description }

find

• find first instance of
• returns one value

array = [23, 56, 22, 17, 85]

value = array.find do |item|
    item > 23
end

puts "value found #{value}"

Can also be written as

value = [23, 56, 22, 17, 85].find { |item| item > 23 }

puts "value found #{value}"

Using the Person class from earlier

result = people.find do |person|
    person.salary > 65000
end

puts result.description

enumerators.rb

array = Array.new(10) { rand(1...100) }

puts 'starting array of random numbers'
print array
puts
selected_numbers = array.select do |number|
    number > 50
  end
puts 'selected numbers'
print selected_numbers
puts

print array
puts
print array.sort
puts




array = ['4', '23', '45', '2', '19']
puts 'before sort'
print array
puts
puts 'default sort'
print array.sort
puts
puts 'custom sort'
print array.sort { |x, y| x.to_i <=> y.to_i }
puts


# change the x and y to see what happens

person.rb

# class to demo ruby features
class Person
  attr_reader :name, :job_title, :phone, :salary

  @employee_number = 0
  def initialize(name, job_title, phone, salary)
    @name = name
    @job_title = job_title
    @phone = phone
    @salary = salary.to_i
    @number = Person.increase_number
  end

  def self.increase_number
    @employee_number += 1
  end

  def description
    "##{@number} #{@name} is a #{@job_title} and has salary #{@salary}"
  end
end

person_enumerators.rb

require_relative 'person'

people = [
            Person.new('Kerry MacFarlane', 'developer', '555-1234', '60000'),
            Person.new('Terry Grayson', 'manager', '555-3456', '90000'),
            Person.new('Sam Ferguson', 'developer', '555-4321', '65000'),
            Person.new('Jossef Goldberg', 'designer', '555-2222', '65000'),
            Person.new('Doris Hartwig', 'engineer', '555-6767', '75000'),
            Person.new('Steven Selikoff', 'developer', '555-2424', '65000'),
            Person.new('Zheng Mu', 'developer', '555-5885', '65000'),
            Person.new('Greg Komosinski', 'analyst', '555-9090', '55000')
          ]

selected_people = people.select do |person|
  person.salary > 65_000
end
puts 'selected people'
selected_people.each { |p| puts p.description }

puts 'before sort'

people.each { |p| puts p.description }

sorted_people = people.sort { |x, y| y.name <=> x.name }

puts 'after sort'

sorted_people.each { |p| puts p.description }


puts 'find person'
result = people.find do |person|
  person.salary > 65_000
end

puts result.description


# Refactor the above code to create helper methods to do the following
# - display an array of person objects
# - select people in an array of person objects based on a minimum 
#      and maximum salary
# - find a person of a particular salary value in an array of person objects 
# - sort poeple by name
# - sort people by salary
# - get the person with the highest salary
# - get the person with the lowest salary

# Write code to call each of the above methods. 
# The code should a couple examples of the select and find methods,
# including when there are no resultsd.