is there an itertor of chunks?

[Skaperen]

i have a list (or tuple) of many items. here is a very simple case:

foo = (9,8,7,6,5,4,3,2,1,0)

what i want to do is step through the list with a step of 1 and a chunk of 3:

foo = (9,8,7,6,5,4,3,2,1,0)
print('welcome to foo')
for x in stepchunk(foo,1,3):
    print(' '.join(str(y)for y in x))
print('end of foo')

Output:
welcome to foo
9 8 7
8 7 6
7 6 5
6 5 4
5 4 3
4 3 2
3 2 1
2 1 0
end of foo

this can be done with a more complex expression that does its own indexing and slicing (BTDT). i'd like to know if there is some simpler form in the existing library, before i go to write my own. also, what should i name this function if not "stepchunk"? it would be a generator.

[ndc85430]

The third party library Toolz has a function called sliding_window: https://toolz.readthedocs.io/en/latest/a...ing_window to do this:

>>> import toolz
>>> list(toolz.itertoolz.sliding_window(3, foo))
[(9, 8, 7), (8, 7, 6), (7, 6, 5), (6, 5, 4), (5, 4, 3), (4, 3, 2), (3, 2, 1), (2, 1, 0)]

[buran]

more_iterools.windowed

[Pedroski55]

Simple one-size

foo = [9,8,7,6,5,4,3,2,1,0]
for i in range(2, len(foo)):
    print(foo[i-2], foo[i-1], foo[i])

or variable size

chunk_size = input('How big do you like your chunks, Hunk? ')
size = int(chunk_size)
   
indexes = [j for j in range(size, 0, -1)]

for i in range(size, len(foo) + 1):
    mylist = []
    for j in indexes:
        num = i-j
        mylist.append(foo[num])
    print(mylist)

[deanhystad]

def stepchunk(items, step, chunk_size):
    """Generate overlapping slices of items using a loop."""
    for i in range(0, len(items)-chunk_size+1, step):
        yield(items[i:i+chunk_size])

def stepchunk2(items, step, chunk_size):
    """Return a generator that generates overlapping slices of items using zip."""
    return zip(*[items[i*step:] for i in range(chunk_size)])

for x in stepchunk((9,8,7,6,5,4,3,2,1,0), 1, 3):
    print(x)

for x in stepchunk2((9,8,7,6,5,4,3,2,1,0), 1, 3):
    print(x)

[perfringo]

i'd like to know if there is some simpler form in the existing library,

Built-in itertools provide recipe grouper (Collect data into non-overlapping fixed-length chunks or blocks).

[Skaperen]

Built-in itertools provide recipe grouper (Collect data into non-overlapping fixed-length chunks or blocks).

the closest thing i see in there is pairwise() which only does chunks of 2 (as far as i can see). what if i want chunks of size chunk_len?

[deanhystad]

None of the itertools do what you want, but at the bottom of the page there are recipes that show how to use itertools to make other tools. grouper does not do what you want, but sliding_window does.

[Skaperen]

None of the itertools do what you want, but at the bottom of the page there are recipes that show how to use itertools to make other tools. grouper does not do what you want, but sliding_window does.

for a step interval of 1 it looks like it can do that. but what if i want a step interval of N? oh wait, selecting every Nth item of the returned list would be that for a step interval of N. let's see, now, how to slice an interval of N.