determining which value is the first to appear five times in a list?

Chris Colbert sccolbert at
Sat Feb 6 19:24:21 CET 2010

I'm working on a naive K-nearest-neighbors selection criteria for an optical
character recognition problem.

After I build my training set, I test each new image against against the
trained feature vectors and record the scores as follows:

match_vals = [(match_val_1, identifier_a), (match_val_2, identifier_b) ....
] and so on..

then I sort the list so the smallest match_val's appear first (indictating a
strong match, so I may end up with something like this:

[(match_val_291, identifier_b), (match_val_23, identifier_b), (match_val_22,
identifer_k) .... ]

Now, what I would like to do is step through this list and find the
identifier which appears first a K number of times.

Naively, I could make a dict and iterate through the list AND the dict at
the same time and keep a tally, breaking when the criteria is met.

such as:

def getnn(match_vals):
    tallies = defaultdict(lambda: 0)
    for match_val, ident in match_vals:
        tallies[ident] += 1
        for ident, tally in tallies.iteritems():
            if tally == 5:
                return ident

I would think there is a better way to do this. Any ideas?


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