Max M wrote: >> depending on the data, it might be more efficient to store the >> "last seen index" in a dictionary, and sort the result on the way >> out (if necessary). something like > > form sets import Set > > data = list(Set([0.1,0.5,0.6,0.4,0.1,0.5,0.6,0.9])) read the OP's spec again. </F>