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    Is the input always sorted (or at least collated) on the first column (which is sometimes the only column)?  Is the second column always either 1 or blank?  Please do not respond in comments; edit your question to make it clearer and more complete. Commented Oct 12, 2017 at 19:36
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    Great that you've detailed the input. Could you update the question to clearly show desired output ? Commented Oct 12, 2017 at 21:14