[FIXED] Splitting a list on non-sequential numbers

Issue

I have an ordered list of entities, numbered in a broken sequence:

[1, 2, 3, 6, 7, 11, 17, 18, 19]

I'd like to break the list where there's a gap, and collect the results in a new list:

[[1, 2, 3], [6, 7], [11], [17, 18, 19]]

I have the feeling there's a name for what I want to do and probably a nice library function for it - but I can't think of it. Can anyone shine some light before I possibly reinvent a wheel?

---

edit: Thanks, folks, but I was asking if there's a name for this operation and an existing algorithm, not for implementations - this is what I came up with:

def group_adjoining(elements, key=lambda x: x):
    """Returns list of lists of contiguous elements

    :key: function to get key integer from list element
    """
    if not elements:
        return elements

    result = [[elements[0]]]

    for a, b in zip(elements, elements[1:]):
        if key(a) + 1 == key(b):
            result[-1].append(b)
        else:
            result.append([b])

    return result

Solution

I first came across more_itertools today, and I think this package is useful for this problem.

pip install more-itertools

from more_itertools import split_when

l = [1, 2, 3, 6, 7, 11, 17, 18, 19]
res = list(split_when(l, lambda a, b: a + 1 != b))
print(res)

Answered By - gypark