drop_duplicates() does not drop duplicates of large datasets
I'm trying to remove the duplicates contained in this following text file:
https://www.dropbox.com/s/mx3zqot352gdrhq/hg19.txt?dl=0
After reading this into a dataframe, and calling drop_duplicates, the dataframe still has the same number of rows. Though clearly, there are many duplicates contained in the file.

I am using a Mac with 8 gigs of RAM. I'm not sure why this is occurring.
