[Python-ideas] Run length encoding

[Neal Fultz]

Whoops, scratch that part about encode /decode.

On Sat, Jun 10, 2017 at 8:33 PM, Neal Fultz <nfultz at gmail.com> wrote:

> Yes, I mean zip compression :)
>
> Also, everyone's been posting decode functions, but encode is a bit harder
> :).
>
> I think it should be equally easy to go one direction as the other.
> Hopefully this email chain builds up enough info to update the docs for
> posterity / future me.
>
> On Sat, Jun 10, 2017 at 8:27 PM, Joshua Morton <joshua.morton13 at gmail.com>
> wrote:
>
>> David: You're absolutely right, s/2/3 in my prior post!
>>
>> Neal: As for why zip (at first I thought you meant the zip function, not
>> the zip compression scheme) is included and rle is not, zip is (or was), I
>> believe, used as part of python's packaging infrastructure, hopefully
>> someone else can correct me if that's untrue.
>>
>> --Josh
>>
>> On Sat, Jun 10, 2017 at 8:20 PM David Mertz <mertz at gnosis.cx> wrote:
>>
>>> 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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