functional programming with map()
amuys at shortech.com.au
Tue Feb 26 00:45:41 CET 2002
Paul Rubin <phr-n2002a at nightsong.com> wrote in message news:<7xbseeayxk.fsf at ruckus.brouhaha.com>...
> "Emile van Sebille" <emile at fenx.com> writes:
> > "Paul Rubin"
> > > Both of those build up a new list of the results, instead of
> > > discarding the values. If the f function takes an integer and
> > > computes a 20-megabyte structure, you've got a problem.
> > If you know it's coming, throw it away first:
> > [x.f() and None for x in items]
> OK, but that buidls a list of None as long as the item list. Not
> so bad, since it gets reclaimed right away, but still unsatisfying.
> > filter(None,[x.f() and None for x in items])
> > returns an empty list vs 0 for the reduce.
> Again there's this intermediate list that's as long as the original list.
> Do you see a way around that?
filter(lambda x:x.f() and 0, items) ?
It's identical to the the reduce method posted previously, but avoids
the tuple indexing required by reduce's use of a binary operator vs.
Of course my first preference would be the list comprehension,
discarding the redundant list, and if that was prohibitively expensive
falling back to the original imperative style.
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