issue_comments

This should now behave correctly with optional indexes.

This is ready for another round of review.

I've changed the signature of reset_index to option C. It is also almost ready for #1017 (just added two small TODOs).

Did you go for allowing set_index() to rename variables?

Not yet, but as you said we could safely add this later.

Just committed review changes.

.reset_index() doesn't accept kwargs anymore, though I don't know what to choose between the options below (currently option A is implemented): - option A: reset_index(dim, levels=None) where dim may accept multiple dimension names (in that case levels must be a list of lists with the same length than dim, or simply None that would then be applied to all given dimensions). - option B: same than option A, reset_index(dim, levels=None), except that dim only accepts one dimension (thus a bit simpler but less flexible). - option C: reset_index(dim_or_levels) where one can provide a list of dimension(s) and/or level(s). This is the most flexible and concise, though maybe less readable. Allow providing both dimensions and levels may be ambiguous too.

if x is a normal (non-multi) Index, array.reset_index('x') is not well defined

Currently .reset_index() doesn't allow resetting normal indexes, but we can wait for #1017 before merging this.

Sorry for the delay @shoyer. I've read your comments above and they all seem relevant. I'll find some time next week to get back on this.

Some API design questions (mostly from @shoyer's review) we need to fix: - We need to choose whether to use dim=indexes kwargs or fixed arg/kwarg relative to a given dimension for the signatures of .set_index(), .reset_index() and .reorder_levels(). - Do we also allow .set_index() to rename the dimension(s) if needed, instead of doing .set_index(...).rename(...) ? Is this a common use case that is worth it? - After discussion in #1017, it seems that we need an easy way to (re)set indexes either to no index or to range(n).

For point 1, my preference goes to dim=indexes kwargs, especially if we need 2 and 3. It's less succinct, but it's more close to the signatures of other xarray methods like .reindex() or .sel(), and it allows (re)setting the indexes of multiple dimensions in a single call. Given 2, I find set_index(new_dim_name=['level_1', 'level_3']) a bit more elegant than set_index(['level_1', 'level_2'], name='new_dim_name'). Given 3, array.reset_index('x') seems ambiguous compared to array.reset_index(x=None) (no index) and, e.g., array.reset_index(x='range') (range(n) index).