voleinikov

# Adapted from StackOverflow answers:
# http://stackoverflow.com/a/8477067/1319740
# and
# http://stackoverflow.com/a/18113090/1319740
# With help from:
# http://technicalpickles.com/posts/parsing-csv-with-ruby/

# A small rake task that validates that all required headers are present in a csv
# then converts the csv to an array of hashes with column headers as keys mapped 
# to relevant row values. 

voleinikov

# Given a float weight between 0 and 1, returns true that percentage of the time 
# e.g. 10.times { weighted_bool 0.3 } # should return true about 3 times 

def weighted_bool true_weight = 0.5
  raise ArgumentError.new("Weight must be a positive value less than or equal to 1.0") unless true_weight >= 0 and true_weight <= 1.0
  return rand <= true_weight
end

voleinikov

In views/users/show.html.erb
<ul>
<%= render @user.posts %>
</ul>

Meanwhile make views/posts/_post.html.erb and in that file have something like
<li> <%= post.body %> </li>

voleinikov

# Length acts as an array method and gives the correct record count. 
1.9.3-p362 :028 > u.clicks.select(:user_id).uniq.length
  Click Load (0.4ms)  SELECT DISTINCT user_id FROM "clicks" WHERE "clicks"."url_id" = 4
 => 2 

# Here .count is being used by Active Record and inserted into the generated SQL and is not an array method.  It gives a wrong answer.
1.9.3-p362 :029 > u.clicks.select(:user_id).uniq.count
   (0.4ms)  SELECT DISTINCT COUNT("clicks"."user_id") FROM "clicks" WHERE "clicks"."url_id" = 4
 => 3 

voleinikov

[:a, :b].product([1,2]) # >>> [[:a, 1], [:a, 2], [:b, 1], [:b, 2]]
[:a, :b].product(1,2,3]) # >> [[:a, 1], [:a, 2], [:a, 3], [:b, 1], [:b, 2], [:b, 3]]

voleinikov

#Ex:
a = []
b = [1,2,3]
a.unshift(b) #>> gives you a = [[1,2,3]]

# If you instead use the splat it will give you
a.unshift(*b) #>> gives you [1,2,3]

voleinikov

# Array = [1,2,-2,1,0], return array of arrays of pairs of indicies of the values that add up to zero

def pairs(array) 
  pairs = []
  traverse = array.count
  
  traverse.times do |i|
    traverse.times do |j|
      # We don't want to check cases where the j value is behind the i value or at the same position
      # Because we don't want to re-check past values or check the same value

voleinikov

# Class counting example.rb

# An example of using a hash to count attributes stored in a class.

class Course
  attr_accessor :name, :dept, :credits

	def initialize (name, dept, credits)
		@name = name
		@dept = dept

voleinikov

class Array

  #  In methods, my_map, my_inject, and my_select, you should have just used your my_each method instead of using the while loop.  Would make slightly cleaner results, plus you made it so you might as well use it!

  def my_map(&proc)
    i = 0
    new_array = []
    while i < self.length
      new_array << proc.call(self[i])
      i += 1

voleinikov

class Student
  attr_accessor :name

  def initialize(first_name, last_name)
    @name = "#{first_name} #{last_name}"
  end

  def courses
    Course.get_courses(self)
  end