How to remove the innermost level of nesting in a list of lists of varying lengths

Question

I\'m trying to remove the innermost nesting in a list of lists of single element length lists. Do you know a relatively easy way (converting to NumPy arrays is fine) to get

Answer 1

If the nesting is always consistent, then this is trivial:

In [2]: import itertools

In [3]: nested = [ [ [1],[2],[3],[4], [5] ], [ [6],[7],[8] ] , [ [11],[12] ] ]

In [4]: unested = [list(itertools.chain(*sub)) for sub in nested]

In [5]: unested
Out[5]: [[1, 2, 3, 4, 5], [6, 7, 8], [11, 12]]

Note, the solutions that leverage add with lists are going to give you O(n^2) performance where n is the number of sub-sublists that are being merged within each sublist.