From: Greg Willits <lists@...>
Date: 2012-04-20T19:34:04+09:00
Subject: Re: finding duplicates in an array and its index number

I do a lot of indexing of data. Usually they're multi-field records, and 
each data set will have multiple indexes. The technique I use is below. 
This indexes all elements of the array. So, then to find duplicates, you 
have to loop again to find array counts > 1. Anyway, it's a slightly 
different way to do it in the event an index of all entries would be 
useful for lookups.


data      = [1, 2, 3, 1, 3, 4, 6, 5, 4]
dataIndex = {}

data.each_with_index do |value, indx|

  index_key = value
  index_value = indx

  if !dataIndex.has_key?(index_key)
    dataIndex.store(index_key, [])
  end

  dataIndex[index_key].push(index_value)
end

p dataIndex

dataIndex.each do |key, indxs|
  if indxs.count > 1
    # do something
    puts "#{key} appears at #{indxs.join(', ')}"
  end
end

-- gw

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