[Python-ideas] Run length encoding

[David Mertz]

God no! Not in the Python 2 docs! ... if the recipe belongs somewhere it's
in the Python 3 docs.  Although, I suppose it could go under 2 also, since
it's not actually a behavior change in the feature-frozen interpreter.  But
as a Python instructor (and someone who remembers the cool new features of
Python 1.5 over 1.4 pretty well), my attitude about Python 2 is "kill it
with fire!"

Your spelling of the one-liner is prettier, shorter, and more intuitive
than mine, and the same speed.

On Sat, Jun 10, 2017 at 8:12 PM, Joshua Morton <joshua.morton13 at gmail.com>
wrote:

> Another is
>
> [(k, len(list(g))) for k, g in groupby(l)]
>
>
> It might be worth adding it to the list of recipies either at
> https://docs.python.org/2/library/itertools.html#itertools.groupby or at
> https://docs.python.org/2/library/itertools.html#recipes, though.
>
> On Sat, Jun 10, 2017 at 8:07 PM David Mertz <mertz at gnosis.cx> wrote:
>
>> Here's a one-line version:
>>
>> from itertools import groupby
>> rle_encode = lambda it: (
>>     (l[0],len(l)) for g in groupby(it) for l in [list(g[1])])
>>
>> Since "not every one line function needs to be in the standard library"
>> is a guiding principle of Python, and even moreso of `itertools`, probably
>> this is a recipe in the documentation at most.  Or maybe it would have a
>> home in `more_itertools`.
>>
>>
>> On Sat, Jun 10, 2017 at 7:20 PM, Neal Fultz <nfultz at gmail.com> wrote:
>>
>>> Hello python-ideas,
>>>
>>> I am very new to this, but on a different  forum and after a couple
>>> conversations, I really wished Python came with run-length encoding
>>> built-in; after all, it ships with zip, which is much more complicated :)
>>>
>>> The general idea is to be able to go back and forth between two
>>> representations of a sequence:
>>>
>>> [1,1,1,1,2,3,4,4,3,3,3]
>>>
>>> and
>>>
>>> [(1, 4), (2, 1), (3, 1), (4, 2), (3, 3)]
>>>
>>> where the first element is the data element, and the second is how many
>>> times it is repeated.
>>>
>>> I wrote an encoder/decoder in about 20 lines (
>>> https://github.com/nfultz/rle.py/blob/master/rle.py ) and would like to
>>> offer it for the next version; I think it might fit in nicely in the
>>> itertools module, for example. I am curious about your thoughts.
>>>
>>> Best,
>>>
>>> -Neal
>>>
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>>>
>>
>>
>> --
>> Keeping medicines from the bloodstreams of the sick; food
>> from the bellies of the hungry; books from the hands of the
>> uneducated; technology from the underdeveloped; and putting
>> advocates of freedom in prisons.  Intellectual property is
>> to the 21st century what the slave trade was to the 16th.
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>


-- 
Keeping medicines from the bloodstreams of the sick; food
from the bellies of the hungry; books from the hands of the
uneducated; technology from the underdeveloped; and putting
advocates of freedom in prisons.  Intellectual property is
to the 21st century what the slave trade was to the 16th.
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