string = "Now is the time"
puts string.at(2)  #=> "w"
puts string.from(8)  #=> "he time"
puts string.to(8)  #=> "Now is th"
puts string.first  #=> "N"
puts string.first(3)  #=> "Now"
puts string.last  #=> "e"
puts string.last(4)  #=> "time"
 
puts string.starts_with?("No")  #=> true
puts string.ends_with?("ME")  #=> false
 
count = Hash.new(0)
string.each_char { |ch | count[ch] += 1 }  
#=> {" " => 3, "w" => 1, "N" => 1, "o" => 1, "e" => 2, "h" => 1, "s" => 1, "t" => 2, "i" => 2 }

Inflector.inflections do |inflect|
  inflect.plural(/-in-law$/, "s-in-law")
  inflect.singular(/s-in-law$/, "-in-law")
  inflect.uncountable("air", "information", "water")  #no singular form, no plural form
end

puts 3.ordinalize  #=> "3rd"
puts 321.ordinalize  #=> "321st"
 
puts 20.byes  #=> 20
puts 20.kilobytes  #=> 20480
puts 20.megabytes  #=> 20971520
puts 20.gigabytes  #=> 21474836480
puts 20.terabytes  #=> 21990232555520
puts 20.petabytes  #=> 22517998136852480
puts 1.exabyte  #=> 1152921504606846976
 
puts 20.seconds  #=> 20
puts 20.minutes  #=> 1200
puts 20.hours  #=> 72000
puts 20.days  #=> 1728000
puts 20.weeks  #=> 12096000
puts 20.fortnights  #=> 24192000
puts 20.months  #=> 51840000
puts 20.years  #=> 630720000
 
puts Time.now  #=> Tue May 18 22:03:21 +0800 2010
puts 20.minutes.ago  #=> Tue May 18 21:43:53 +0800 2010
puts 20.hours.from_now  #=> Wed May 19 18:04:11 +0800 2010
puts 20.weeks.from_now  #=> Tue Oct 05 22:04:22 +0800 2010
puts 20.months.ago  #=> Thu Sep 18 22:04:34 +0800 2008
puts 20.minutes.until("2010-12-26 12:00:00".to_time)  #=> Sun Dec 26 11:40:00 UTC 2010
puts 20.minutes.since("2006-11-08 01:15:00".to_time)  #=> Wed Nov 08 01:35:00 UTC 2006

now = Time.now  
puts now  #=>  Tue May 18 22:09:17 0800 2010
puts now.to_date  #=> 2010-05-18
puts now.to_s  #=> Tue May 18 22:09:17 +0800 2010
 
puts now.to_s(:short)  #=> 18 May 22:09
puts now.to_s(:long)  #=> May 18, 2010 22:09
puts now.to_s(:db)  #=> 2010-05-18 22:09:17
puts now.to_s(:rfc822)  #=> Tue, 18 May 2010 22:09:17 +0900
puts now.ago(3600)  #=> Tue May 18 21:09:17 +0800 2010
puts now.at_beginning_of_day  #=> Tue May 18 00:00:00 +0800 2010
 
puts now.at_beginning_of_month  #=> Sat May 01 00:00:00 +0800 2010
puts now.at_beginning_of_week  #=> Mon May 17 00:00:00 +0800 2010
puts now.beginning_of_quarter  #=> Thu Apr 01 00:00:00 +0800 2010
puts now.at_beginning_of_year  #=> Fri Jan 01 00:00:00 +0800 2010
puts now.at_midnight  #=> Tue May 18 00:00:00 +0800 2010
 
puts now.change(:hour => 13)  #=> Tue May 18 13:00:00 +0800 2010
puts now.last_month  #=> Sun Apr 18 22:09:17 +0800 2010
puts now.last_year  #=> Mon May 18 22:09:17 +0800 2009
puts now.midnight  #=> Tue May 18 00:00:00 +0800 2010
puts now.monday  #=> Mon May 17 00:00:00 +0800 2010
 
puts now.months_ago(2)  #=> Thu Mar 18 22:09:17 +0800 2010
puts now.months_since(2)  #=> Sun Jul 18 22:09:17 +0800 2010
puts now.next_week  #=> Mon May 24 00:00:00 +0800 2010
puts now.next_year  #=> Wed May 18 22:09:17 +0800 2011
puts now.seconds_since_midnight  #=> 79757.033881
 
puts now.since(7200)  #=> Wed May 19 00:09:17 +0800 2010
puts now.tomorrow  #=> Wed May 19 22:09:17 +0800 2010
puts now.years_ago(2)  #=> Sun May 18 22:09:17 +0800 2008
puts now.years_since(2)  #=> Fri May 18 22:09:17 +0800 2012
puts now.yesterday  #=> Mon May 17 22:09:17 +0800 2010
 
puts now.advance(:days => 30)  #=> Thu Jun 17 22:09:17 +0800 2010
puts Time.days_in_month(2)  #=> 28
puts Time.days_in_month(2, 2000)  #=> 29

groups = posts.group_by { |post| post.author_id }
 
or
 
groups = post.group_by(&:author_id)