Ruby Listing notes - S ORTING AND FILTERING LISTS IN RUBY...

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SORTING AND FILTERING LISTS IN RUBY Let's say that we have a collection of articles, each of which has an author, creation date, and topic. The obvious  Ruby construct for this is an  array  of  hash es (a  hash  is Ruby's associative array, Python's  dict ). Pretend that  our authors are Joe, Ali, and Bob and they take turns writing about donkeys, earthworms, finches, and crayons. The  Ruby object can be built explicitly like this: articles = [ { :author => "Ali" , :date => "2010-11-27" , :topic => "earthworms" }, { :author => "Joe" , :date => "2011-06-18" , :topic => "donkeys" }, { :author => "Ali" , :date => "2011-06-25" , :topic => "earthworms" }, { :author => "Bob" , :date => "2011-07-12" , :topic => "finches" }, { :author => "Ali" , :date => "2011-07-19" , :topic => "donkeys" }, { :author => "Joe" , :date => "2011-08-02" , :topic => "crayons" }, { :author => "Joe" , :date => "2011-08-16" , :topic => "finches" }, { :author => "Bob" , :date => "2011-08-18" , :topic => "earthworms" } ] Now let's say we just want to do something with all of Joe's articles. There's a method on Ruby array s just for that,  called  select . An expression goes in curly braces which returns true or false for whether or not to include a given 
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