Dear everyone in the Mailing list:
 
It is easy to get the unique elements in a column. But I would like to get rid of those rows that the elements of this column are redundant. Or sometimes, to have a look at the rows that the elements of this column are redundant is also important. I guess it boils down to throw out the index of the redundant elements. 
 
With millions of rows, how can I efficiently perform the task?
 
Thank you in advance.
 
Boshao


      
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