issue_comments

transpose_coords is used to transpose coordinates with multiple dimensions: ```python In [1]: import xarray as xr ...: ...: ds = xr.tutorial.open_dataset("rasm") ...: ds.Tair.attrs.clear() ...: ds.Tair Out[1]: <xarray.DataArray 'Tair' (time: 36, y: 205, x: 275)> [2029500 values with dtype=float64] Coordinates: * time (time) object 1980-09-16 12:00:00 ... 1983-08-17 00:00:00 xc (y, x) float64 ... yc (y, x) float64 ... Dimensions without coordinates: y, x

In [2]: ds.Tair.transpose("x", "y", ..., transpose_coords=False) Out[2]: <xarray.DataArray 'Tair' (x: 275, y: 205, time: 36)> [2029500 values with dtype=float64] Coordinates: * time (time) object 1980-09-16 12:00:00 ... 1983-08-17 00:00:00 xc (y, x) float64 ... yc (y, x) float64 ... Dimensions without coordinates: x, y

In [3]: ds.Tair.transpose("x", "y", ..., transpose_coords=True) Out[3]: <xarray.DataArray 'Tair' (x: 275, y: 205, time: 36)> [2029500 values with dtype=float64] Coordinates: * time (time) object 1980-09-16 12:00:00 ... 1983-08-17 00:00:00 xc (x, y) float64 ... yc (x, y) float64 ... Dimensions without coordinates: x, y `` Interestingly,transpose_coordsis only an option forDataArray.transpose, and it defaults toTrue`. This means that the example from https://github.com/pydata/xarray/issues/7294#issue-1452123685 always does the same thing, so even if we did implement the reordering nothing would change.

As such, I'm -0.5 on changing the order in which the coordinates are stored, since the only time that order is used is the repr / HTML repr. In the past we have actually considered sorting the coordinates alphabetically, which did not happen because the coordinate names can be hashables of arbitrary types, and comparing a pair of hashables of different types is not easy.

Just noticed that the same logic does not work for Datasets, since all variables are kept in a common dict and the information about which are coordinates and which are data-variables is kept in a set, which is not ordered...

The logic for this is not really trivial unless I am missing some obvious trick. You basically have to change the loop here: https://github.com/pydata/xarray/blob/ff6793d975ef4d1d8d5d32b8ad6f4f44e02dda9b/xarray/core/dataarray.py#L2919 To loop first over the new dims and potential coordinates with the same name and then over the rest of the coordinates (If possible in a single loop without code repetition).

Feel free to propose a PR!

And what should happen with non-dimension coordinates? Should they simply end up in the end?

Thanks. On one hand I see your point: a mapping does not ensure order. On the other hand, is it not counter-intuitive that the order of the dictionary-like container coords is not changed when using transpose_coords=True?

Here my reasoning: - dictionaries maintain insertion order - coords are a "Dictionary-like container" - a coords dict is created when transpose_coords==True - would it not be the right time, during insertion, to create the proper order?

The coordinates are just a mapping from names to DataArrays, I don't think the order has any meaning (like it does for normal dicts).