What duplicates are you talking about. LR only shows images that have been imported to it, that you have made adjustments to in an external editor and selected to add to the catalog, made virtual copies of or copied a bunch of images to some other folder on your drive and Re-Imported them.
So if you are seeing duplicates of images the you have done one of the 4 things listed above.
To sort images so that any duplicates are right next to one another select to sort by Capture time. Unless you have changed that in the duplicate images they will all be sorted by date and time of capture no matter when they were imported.