Inefficient summing

[Alexander Schmolck]

beginner <zyzhu2000 at gmail.com> 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)))

? 

:)