issue_comments

This should now behave correctly with optional indexes.

Can we update this for optional indexes? (now on master)

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.

I kind of like Option C, given that we have guaranteed level names and variables to have no conflicts.

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

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.

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().

For set_index and reorder_levels, I like the kwargs or a dictionary. It's nice and explicit. But for reset_index, I think we probably want a list.

It's not at all obvious to me what array.reset_index(x=None) does. It could just as easily mean "reset nothing from x" as "reset x to have a null index". In fact, the former seems more consistent with how we handle levels. In contrast, array.reset_index(['x']) pretty clearly means that the 'x' index should be reset.

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?

My inclination is yes -- this feels like a common thing to do. But we could also safely add this later.

After discussion in #1017, it seems that we need an easy way to (re)set indexes either to no index or to range(n).

We definitely need a way to reset indexes to the default, but after #1017, I'm not sure we will need a way to set them to range(n).

Unfortunately, if x is a normal (non-multi) Index, array.reset_index('x') is not well defined. We need a name for the variable that was formerly named x (or could drop it, e.g., with array.reset_index('x', drop=True) or array.drop('x')), otherwise it will still be the index for the x-axis. Or, I suppose we could rename the x dimension to something else.

One option is to add some sort of prefix or suffix to the index name when it becomes a new variable, e.g., array.reset_index('x') renames the coordinate x to x_. This seems like a probably safe choice, though I hate to add more automatic names to the API.

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).