CODEWITHSUNDEEP
pythonpython-2.7list
diegus
diegus

Reputation: 1188

Python: concatenate all consecutive sublists of a list until a condition is met

I have a list containing sublists elements that look like this:

li = [[1],[2,3,4],[5,6],[7,8,9,10],[11],[12],[13],[14,15,16]]

I would like to concatenate all the sublists that are shorter than a certain value limit with the next sublists until the length of the new sublist is >= limit

Examples:

if limit=3 the previous list should became:

li_result = [[1,2,3,4], [5,6,7,8,9,10], [11,12,13], [14,15,16]]

if limit=2 the previous list should became:

li_result = [[1,2,3,4], [5,6] [7,8,9,10], [11,12], [13,14,15,16]]

if limit=1 the previous list should became:

li_result = [[1],[2,3,4],[5,6],[7,8,9,10],[11],[12],[13],[14,15,16]]

To concatenate I could use from 

 itertools import chain
 list(chain.from_iterable(li)

How would I limit the concatenation based on my limit value?

Upvotes: 1

Views: 333

Answers (3)

Mykola Zotko
Mykola Zotko

Reputation: 17794

You can use the function accumulate():

def func(l, limit): 
    acc = list(accumulate(l, lambda x, y: x + y if len(x) < limit else y))
    res = list(filter(lambda x: len(x) >= limit, acc))
    if len(acc[-1]) < limit:
        res.append(acc[-1])
    return res

Test:

l = [[1],[2,3,4],[5,6],[7,8,9,10],[11],[12],[13],[14,15,16]]
print(func(l, 3))
# [[1, 2, 3, 4], [5, 6, 7, 8, 9, 10], [11, 12, 13], [14, 15, 16]]

print(func(l, 2))
# [[1, 2, 3, 4], [5, 6], [7, 8, 9, 10], [11, 12], [13, 14, 15, 16]]

print(func(l, 1))
# [[1], [2, 3, 4], [5, 6], [7, 8, 9, 10], [11], [12], [13], [14, 15, 16]]

l = [[1,2,3],[4]]
print(func(l, 3))
# [[1, 2, 3], [4]]

l = [[1],[2]]
print(func(l, 3))
# [[1, 2]]

Upvotes: 0

Yam Mesicka
Yam Mesicka

Reputation: 6581

This one might work:

from typing import Any, List

def combine_to_max_size(l: List[List[Any]], limit: int) -> List[List[Any]]:
    origin = l[:]  # Don't change the original l
    result = [[]]
    while origin:
        if len(result[-1]) >= limit:
            result.append([])
        result[-1].extend(origin.pop(0))
    return result

Few tests:

l = [[1],[2, 3],[4, 5, 6]]
assert combine_to_max_size(l, 1) == [[1], [2, 3], [4, 5, 6]]
assert combine_to_max_size(l, 2) == [[1, 2, 3], [4, 5, 6]]
assert combine_to_max_size(l, 4) == [[1, 2, 3, 4, 5, 6]]
assert l == [[1],[2, 3],[4, 5, 6]]

This solution contains typing annotations. To use in Python 2.7, replace

def combine_to_max_size(l: List[List[Any]], limit: int) -> List[List[Any]]:

With:

def combine_to_max_size(l, limit):
    # type: (List[List[Any]], int) -> List[List[Any]]

Upvotes: 2

Thierry Lathuille
Thierry Lathuille

Reputation: 24232

I would simply go with a loop:

def limited_concat(li, limit):
    if not li:
        return []
    out = [[]]
    for sublist in li:
        if len(out[-1]) < limit:
            out[-1].extend(sublist)
        else:
            out.append(sublist[:])
    return out


li = [[1],[2,3,4],[5,6],[7,8,9,10],[11],[12],[13],[14,15,16]]
limited_concat(li, 2)
# [[1, 2, 3, 4], [5, 6], [7, 8, 9, 10], [11, 12], [13, 14, 15, 16]]

Upvotes: 2

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