Introduce ["nested."] for flatten representation

[hombit]

Feature request

Maybe it is a weird idea, but we can provide a new interface for "flat" representation of a nested series within NestedFrame, using dot-prefix:

ndf["nested."] = flat_with_the_matched_index
assert_frame_equal(ndf["nested."], flat_with_the_matched_index)

It would simplify flattening and nesting (no add_nested) in simple cases.

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• I have described the purpose of the suggested change, specifying what I need the enhancement to accomplish, i.e. what problem it solves.
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[wilsonbb]

Maybe we could have ndf["nested.flat"] with support for the shorthand of ndf["nested._"]

[hombit]

Other options are ndf["nested.[]"] or ndf["nested.__flat__"]

[hombit]

One more option is pseudo-methods, like ndf["nested.flat()"]

[dougbrn]

Do we even need a convention? If a dataframe is assigned to a new base level column, it's probably sensible that nested-pandas would want to nest it. Could we just try the nest?

ndf["nested"] = flat_with_the_matched_index

[hombit]

@dougbrn It is a good idea! It would be a bit weird if the flat data frame has a single column, because pandas kinda supports that operation, but I think it would be still nice to have!