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@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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