Question

I have a hash like so:

[
  {
    :lname => "Brown",
    :email => "[e-mail]",
    :fname => "James"
  },
  {
    :lname => nil,
    :email => "[e-mail]",
    :fname => nil
  },
  {
    :lname => "Smith",
    :email => "[e-mail]",
    :fname => "Brad"
  },
  {
    :lname => nil,
    :email => "[e-mail]",
    :fname => nil
  },
  {
    :lname => "Smith",
    :email => "[e-mail]",
    :fname => "Brad"
  },
  {
    :lname => nil,
    :email => "[e-mail]",
    :fname => nil
  }
]

What I would like to learn how to do is how to remove a record if it is duplicate. Meaning, see how there are several “[e-mail]” how can I remove the duplicate records, meaning remove all the others that have an email of “[e-mail]”…. Making email the key not the other fields?

Answer 1

I know this is an old thread, but Rails has a method on ‘Enumerable’ called ‘index_by’ which can be handy in this case:

list = [
  {
    :lname => "Brown",
    :email => "[e-mail]",
    :fname => "James"
  },
  {
    :lname => nil,
    :email => "[e-mail]",
    :fname => nil
  },
  {
    :lname => "Smith",
    :email => "[e-mail]",
    :fname => "Brad"
  },
  {
    :lname => nil,
    :email => "[e-mail]",
    :fname => nil
  },
  {
    :lname => "Smith",
    :email => "[e-mail]",
    :fname => "Brad"
  },
  {
    :lname => nil,
    :email => "[e-mail]",
    :fname => nil
  }
]

Now you can get the unique rows as follows:

list.index_by {|r| r[:email]}.values

To merge the rows with the same email id.

list.group_by{|r| r[:email]}.map do |k, v|
  v.inject({}) { |r, h| r.merge(h){ |key, o, n| o || n } }
end

Custom but efficient method:

list.inject({}) do |r, h| 
  (r[h[:email]] ||= {}).merge!(h){ |key, old, new| old || new }
  r
end.values