[Python-ideas] Run length encoding

[Neal Fultz]

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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>>>>>
>>>>>
>>>>
>>>>
>>>> --
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>>>> 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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