Efficient comparison of 100.000 vectors

Question

I save 100.000 Vectors of in a database. Each vector has a dimension 60. (int vector[60])

Then I take one and want present vectors to the user in order of decreasing sim

Answer 1

Uh, no?

You only have to do all 99,999 against the one you picked (rather than all n(n-1)/2 possible pairs), of course, but that's as low as it goes.

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Looking at your response to nsanders's answer, it is clear you are already on top of this part. But I've thought of a special case where computing the full set of comparisons might be a win. If:

• the list comes in slowly (say your getting them from some data acquisition system at a fixed, low rate)
• you don't know until the end which one you want to compare to
• you have plenty of storage
• you need the answer fast when you do pick one (and the naive approach isn't fast enough)
• Looks are faster than computing

then you could pre-compute the as the data comes in and just lookup the results per pair at sort time. This might also be effective if you will end up doing many sorts...