How to count duplicate elements in a Ruby array

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The following code prints what you asked for. I’ll let you decide on how to actually use to generate the hash you are looking for:

# sample array
a=["aa","bb","cc","bb","bb","cc"]

# make the hash default to 0 so that += will work correctly
b = Hash.new(0)

# iterate over the array, counting duplicate entries
a.each do |v|
  b[v] += 1
end

b.each do |k, v|
  puts "#{k} appears #{v} times"
end

Note: I just noticed you said the array is already sorted. The above code does not require sorting. Using that property may produce faster code.

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