Beam throws an error at submission time in Python if you pass a single PCollection to Flatten. The scenario you describe concerns a one-element list.
On Thu, Mar 21, 2024, 13:43 Joey Tran <joey.t...@schrodinger.com> wrote: > I think it'd be quite surprising if beam.Flatten would become equivalent > to FlatMap if passed only a single pcollection. One use case that would be > broken from that is cases where someone might be flattening a variable > number of pcollections, including possibly only one pcollection. In that > case, that single pcollection suddenly get FlatMapped. > > > > On Thu, Mar 21, 2024 at 4:36 PM Valentyn Tymofieiev via dev < > dev@beam.apache.org> wrote: > >> One possible alternative is to define beam.Flatten for a single >> collection to be functionally equivalent to beam.FlatMap(lambda x: x), but >> that would be a larger change and such behavior might need to be >> consistent across SDKs and documented. Adding a default value is a simpler >> change. >> >> I can also confirm that the usage >> >> | 'Flatten' >> beam.FlatMap(lambda x: x) >> >> is fairly common by inspecting uses of Beam internally. >> On Thu, Mar 21, 2024 at 1:30 PM Robert Bradshaw via dev < >> dev@beam.apache.org> wrote: >> >>> IIRC, Java has Flatten.iterables() and Flatten.collections(), the first >>> of which does what you want. >>> >>> Giving FlatMap a default arg of lambda x: x is an interesting idea. The >>> only downside I see is a less clear error if one forgets to provide this >>> (now mandatory) parameter, but maybe that's low enough to be worth the >>> convenience? >>> >>> On Thu, Mar 21, 2024 at 12:02 PM Joey Tran <joey.t...@schrodinger.com> >>> wrote: >>> >>>> That's not really the same thing, is it? `beam.Flatten` combines two or >>>> more pcollections into a single pcollection while beam.FlatMap unpacks >>>> iterables of elements (i.e. PCollection<Iterable<T>> -> PCollection<T>) >>>> >>>> On Thu, Mar 21, 2024 at 2:57 PM Valentyn Tymofieiev via dev < >>>> dev@beam.apache.org> wrote: >>>> >>>>> Hi, you can use beam.Flatten() instead. >>>>> >>>>> On Thu, Mar 21, 2024 at 10:55 AM Joey Tran <joey.t...@schrodinger.com> >>>>> wrote: >>>>> >>>>>> Hey all, >>>>>> >>>>>> Using an identity function for FlatMap comes up more often than using >>>>>> FlatMap without an identity function. Would it make sense to use the >>>>>> identity function as a default? >>>>>> >>>>>> >>>>>> >>>>>>
