[FIXED] Iterate over all the sub-groups of a list

Issue

Let's say I have a list [1,2,3,4,5,6], and I want to iterate over all the subgroups of len 2 [1,2] [3,4] [5,6].

The naive way of doing it

    L = [1,2,3,4,5,6]
    N = len(L)//2
    for k in range(N):
        slice = L[k*2:(k+1)*2]
        for val in slice:
            #Do things with the slice

However I was wondering if there is a more pythonic method to iterate over a "partitioned" list already. I also accept solutions with numpy arrays. Something like:

    L = [1,2,3,4,5,6]
    slices = f(L,2) # A nice "f" here? 
    for slice in slices:
        for val in slice:
            #Do things with the slice

Thanks a lot!

Solution

Use the grouper recipe from the itertools library:

import itertools

def grouper(iterable, n, fillvalue=None):
    "Collect data into fixed-length chunks or blocks"
    # grouper('ABCDEFG', 3, 'x') --> ABC DEF Gxx"
    args = [iter(iterable)] * n
    return itertools.zip_longest(*args, fillvalue=fillvalue)

L = [1,2,3,4,5,6]
for slice in grouper(L, 2):
    print(slice)

Answered By - Woodford