On 7/19/2020 6:49 PM, David Mertz wrote:
On Sun, Jul 19, 2020 at 6:35 PM Dominik Vilsmeier <dominik.vilsmeier@gmx.de> wrote:

But this looks unnecessarily complicated. Why can't xarray allow the following:

    ds["empty"]["lon", 1:5, "lat", 3:] = 10

which looks very close to the proposed syntax below. Not that I'm against the proposal but I think that any use case involving *only* keyword arguments isn't a very strong one, because it can easily be solved that way without a change to existing syntax.

Xarray already allows positional slices in multiple dimensions.  The existing dict weirdness is to have a way to introduce the named dimensions.  But suppose that the array in question had a first listed 'altitude'.  I think nowadays, we can write:

    arr.loc[50:60, 1:5, 3:]

If we only reference dimensions by number not by name.  Under the "commas separate keys from values" this would be difficult:

    arr.loc[50:60, "lon", 1:5, "lat", 3:]

Yes, I can imagine a rule like "If it is a slice that wasn't preceded by a string, treat it as positional, otherwise if it is a string treat it as a key, but treat the next thing after a string as the slice value corresponding to that key."

That seems more error prone and harder to grok than the potential:

    arr.loc[50:60, lon=1:5, lat=3:]

Where you'd still just have to know that "axis 0 is altitude" of your particular array.

In addition, what if you actually wanted:

arr.loc["lon", "lon", 1:5, "lat", 3:]

That is: what if you have a string argument whose value happens to be name of one of your "named" parameters?