Inefficient summing

Alexander Schmolck a.schmolck at
Thu Oct 9 22:53:52 CEST 2008

beginner <zyzhu2000 at> writes:

> Hi All,
> I have a list of records like below:
> rec=[{"F1":1, "F2":2}, {"F1":3, "F2":4} ]
> Now I want to write code to find out the ratio of the sums of the two
> fields.
> One thing I can do is:
> sum(r["F1"] for r in rec)/sum(r["F2"] for r in rec)
> But this is slow because I have to iterate through the list twice.
> Also, in the case where rec is an iterator, it does not work.

how about:

ratio = (lambda c: c.real/c.imag)(sum(complex(r["F1"], r["F2"] for r in rec)))



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