|  | dropwhile question | | |
| | | Rajanikanth Jammalamadaka |  |
|  Posted: Sat Aug 23, 2008 7:54 pm Post subject: dropwhile question |  |
| Quote: | list(itertools.dropwhile(lambda x: x<5,range(10)))
[5, 6, 7, 8, 9] |
Why doesn't this work?
| Quote: | list(itertools.dropwhile(lambda x: 2<x<5,range(10)))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9] |
Thanks,
Raj
--
"For him who has conquered the mind, the mind is the best of friends;
but for one who has failed to do so, his very mind will be the
greatest enemy."
Rajanikanth |
| |
| | | Marc 'BlackJack' Rintsch | |
| | Posted: Sat Aug 23, 2008 8:12 pm Post subject: Re: dropwhile question | |
On Sat, 23 Aug 2008 14:54:09 -0700, Rajanikanth Jammalamadaka wrote:
| Quote: | list(itertools.dropwhile(lambda x: x<5,range(10)))
[5, 6, 7, 8, 9]
Why doesn't this work?
list(itertools.dropwhile(lambda x: 2<x<5,range(10)))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
|
It *does* work. `dropwhile()` drops as long as the callable returns a
true value and then it stops dropping. First value is 0 and
``2 < 0 < 5`` is `False` so nothing is dropped.
What have you expected?
Ciao,
Marc 'BlackJack' Rintsch |
| |
| | | Fredrik Lundh | |
| | Posted: Sat Aug 23, 2008 8:14 pm Post subject: Re: dropwhile question | |
| |  | |
Rajanikanth Jammalamadaka wrote:
| Quote: | list(itertools.dropwhile(lambda x: x<5,range(10)))
[5, 6, 7, 8, 9]
Why doesn't this work?
list(itertools.dropwhile(lambda x: 2<x<5,range(10)))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
|
it works exactly as specified:
| Quote: | help(itertools.dropwhile)
Help on class dropwhile in module itertools: |
class dropwhile(__builtin__.object)
| dropwhile(predicate, iterable) --> dropwhile object
|
| Drop items from the iterable while predicate(item) is true.
| Afterwards, return every element until the iterable is exhausted.
maybe you meant to use itertools.ifilter?
| Quote: | help(itertools.ifilter)
Help on class ifilter in module itertools: |
class ifilter(__builtin__.object)
| ifilter(function or None, sequence) --> ifilter object
|
| Return those items of sequence for which function(item) is true.
| If function is None, return the items that are true.
| Quote: | list(itertools.ifilter(lambda x: x<5,range(10)))
[0, 1, 2, 3, 4]
list(itertools.ifilter(lambda x: 2<x<5,range(10)))
[3, 4] |
</F> |
| |
| | | Fredrik Lundh | |
| | Posted: Sat Aug 23, 2008 8:28 pm Post subject: Re: dropwhile question | |
Fredrik Lundh wrote:
| Quote: | maybe you meant to use itertools.ifilter?
help(itertools.ifilter)
Help on class ifilter in module itertools:
class ifilter(__builtin__.object)
| ifilter(function or None, sequence) --> ifilter object
|
| Return those items of sequence for which function(item) is true.
| If function is None, return the items that are true.
list(itertools.ifilter(lambda x: x<5,range(10)))
[0, 1, 2, 3, 4]
list(itertools.ifilter(lambda x: 2<x<5,range(10)))
[3, 4]
|
or, more likely, ifilterfalse:
| Quote: | list(itertools.ifilterfalse(lambda x: x<5,range(10)))
[5, 6, 7, 8, 9]
list(itertools.ifilterfalse(lambda x: 2<x<5,range(10)))
[0, 1, 2, 5, 6, 7, 8, 9] |
</F> |
| |
| | | Scott David Daniels | |
| | Posted: Sat Aug 23, 2008 8:41 pm Post subject: Re: dropwhile question | |
Rajanikanth Jammalamadaka wrote:
| Quote: | list(itertools.dropwhile(lambda x: x<5,range(10)))
[5, 6, 7, 8, 9]
Why doesn't this work?
list(itertools.dropwhile(lambda x: 2<x<5,range(10)))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
|
Because it drops _while_ the condition is True (which it is for
the first 0 entries in the sequence). What you want is:
list(x for x in range(10) if 2 < x < 5)
Note that:
list(itertools.dropwhile(lambda x: x<5, range(10)+range(10)))
is [5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
not [5, 6, 7, 8, 9, 5, 6, 7, 8, 9].
--Scott David Daniels
Scott.Daniels.Acm.Org |
| |
| | | Rajanikanth Jammalamadaka | |
| | Posted: Sun Aug 24, 2008 4:07 am Post subject: Re: dropwhile question | |
Thanks for the explanations.
Regards,
Raj
On Sat, Aug 23, 2008 at 3:41 PM, Scott David Daniels
<Scott.Daniels@acm.org> wrote:
| Quote: | Rajanikanth Jammalamadaka wrote:
list(itertools.dropwhile(lambda x: x<5,range(10)))
[5, 6, 7, 8, 9]
Why doesn't this work?
list(itertools.dropwhile(lambda x: 2<x<5,range(10)))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
Because it drops _while_ the condition is True (which it is for
the first 0 entries in the sequence). What you want is:
list(x for x in range(10) if 2 < x < 5)
Note that:
list(itertools.dropwhile(lambda x: x<5, range(10)+range(10)))
is [5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
not [5, 6, 7, 8, 9, 5, 6, 7, 8, 9].
--Scott David Daniels
Scott.Daniels.Acm.Org
--
LINK
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--
"For him who has conquered the mind, the mind is the best of friends;
but for one who has failed to do so, his very mind will be the
greatest enemy."
Rajanikanth |
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