[Python-ideas] Run length encoding

[Joshua Morton]

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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