Your problem looks like 'classification' problem, but as someone said, details about how you want to classify your items are missing.

However you try looking at Wikipedia - Nearest neighbor search
and take a good look at 'Space partitioning'
Take care of items with the sames values.. maybe you shoud 'group' them by default when partitionning your space. If that's not exactly what you wanted try searching 'Classification algorithm' in Google or Wikipedia.