Hi Mark, I think this has already been implemented.
For Iterables (list included), there is `more_itertools.collapse`, which you can use to achieve examples in your code as `list(more_itertools.collapse(list))`. See: https://more-itertools.readthedocs.io/en/stable/api.html#more_itertools.collapse If you don’t mind intermediate conversions: a) For well behaved arrays, such as `numpy.ndarray`, you can do `np.ravel(list).tolist()` or there is a bit more functional `torch.flatten` (I think `numpy` could add this functionality too - it is quite useful). b) For ragged arrays, there is `awkward.flatten`. Given that your need is not related to `numpy.ndarray` objects, I don’t think `numpy` is the right place for it. I would alternatively suggest exploring `more_itertools` and if something is missing, issue `Iterator` related proposals over there. > On 31 Dec 2024, at 06:37, Mark via NumPy-Discussion > <numpy-discussion@python.org> wrote: > > Hello all, > > Many people have asked how to flatten a nested list into a one-dimensional > list (e.g., see this StackOverflow thread > <https://stackoverflow.com/questions/952914/how-do-i-make-a-flat-list-out-of-a-list-of-lists>). > While flattening a 2D list is relatively straightforward, deeply nested > lists can become cumbersome to handle. To address this challenge, I propose > adding a built-in list-flattening functionality to NumPy. > > By adding this feature to NumPy, the library would not only simplify a > frequently used task but also enhance its overall usability, making it an > even more powerful tool for data manipulation and scientific computing. > > The code snippet below demonstrates how a nested list can be flattened, > enabling conversion into a NumPy array. I believe this would be a valuable > addition to the package. See also this issue > <https://github.com/numpy/numpy/issues/28079>. > > from collections.abc import Iterable > > def flatten_list(iterable): > > """ > Flatten a (nested) list into a one-dimensional list. > > Parameters > ---------- > iterable : iterable > The input collection. > > Returns > ------- > flattened_list : list > A one-dimensional list containing all the elements from the input, > with any nested structures flattened. > > Examples > -------- > > Flattening a list containing nested lists: > > >>> obj = [[1, 2, 3], [1, 2, 3]] > >>> flatten_list(obj) > [1, 2, 3, 1, 2, 3] > > Flattening a list with sublists of different lengths: > > >>> obj = [1, [7, 4], [8, 1, 5]] > >>> flatten_list(obj) > [1, 7, 4, 8, 1, 5] > > Flattening a deeply nested list. > > >>> obj = [1, [2], [[3]], [[[4]]],] > >>> flatten_list(obj) > [1, 2, 3, 4] > > Flattening a list with various types of elements: > > >>> obj = [1, [2], (3), (4,), {5}, np.array([1,2,3]), range(3), 'Hello'] > >>> flatten_list(obj) > [1, 2, 3, 4, 5, 1, 2, 3, 0, 1, 2, 'Hello'] > > """ > > if not isinstance(iterable, Iterable) or isinstance(iterable, str): > return [iterable] > > def flatten_generator(iterable): > > for item in iterable: > > if isinstance(item, Iterable) and not isinstance(item, str): > yield from flatten_generator(item) > > else: > yield item > > return list(flatten_generator(iterable)) > > > > _______________________________________________ > NumPy-Discussion mailing list -- numpy-discussion@python.org > To unsubscribe send an email to numpy-discussion-le...@python.org > https://mail.python.org/mailman3/lists/numpy-discussion.python.org/ > Member address: dom.grigo...@gmail.com
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