Also, I think _replace is a bit confusing: the name seems to imply a inplace operation, but it returns a new object without changing the original object.

I think this mea culpa IIRC... I would be very open to consolidating this and .copy into something that returns a (generally shallow) copy of the object with some optional replacements. (The general approach is better than calling a constructor with every attribute, even if the names are not great)

I just checked, and I think the issue can indeed be solved by replacing variable = self with variable = self.copy() (deep=False is the default, so no need to explicitly set it).

Also, I think _replace is a bit confusing: the name seems to imply a inplace operation, but it returns a new object without changing the original object.

My last post was wrong.

I think this part overwrites the attrs,

https://github.com/pydata/xarray/blob/43a2a4bdf3a492d89aae9f2c5b0867932ff51cef/xarray/core/variable.py#L2028 https://github.com/pydata/xarray/blob/43a2a4bdf3a492d89aae9f2c5b0867932ff51cef/xarray/core/variable.py#L2073-L2076

The first line should be replaced by variable = self.copy(deep=False)

~~These lines are suspicious. Maybe we should copy attrs here not geting its reference.~~

https://github.com/pydata/xarray/blob/43a2a4bdf3a492d89aae9f2c5b0867932ff51cef/xarray/core/rolling.py#L498

https://github.com/pydata/xarray/blob/43a2a4bdf3a492d89aae9f2c5b0867932ff51cef/xarray/core/rolling.py#L498

My doubts on this are because self._replace are used elsewhere in the code.

Changing from _replace to copy causes the tests on coarsen to fail, I am looking more into this now.

It seems that a condition of copy is that the data shapes match (variable.py line 947).

If I run ds = xr.tutorial.load_dataset("air_temperature") ds.air.coarsen(lat=5) there is no problem, but once I add a .mean() to the end ds = xr.tutorial.load_dataset("air_temperature") ds.air.coarsen(lat=5).mean()

The error is ValueError: Data shape (2920, 5, 53) must match shape of object (2920, 25, 53)

~I think you are right. _replace calls the constructor with self.variable, ..., fastpath=True which does a direct assignment to DataArray._variable; so you have a new DataArray but with the same underlying data.~ EDIT: Ignore I was looking at dataarray.py; not variable.py

That could be the issue. If it is, you should be able to fix that using python return self.copy(data=func(reshaped, axis=axes, **kwargs))

@dcherian Could this be because the return of variable.py/coarsen or is it likely happening earlier in the fx?

return self._replace(data=func(reshaped, axis=axes, **kwargs))

Yeah. That's true. I did overlook that. Thanks!

Thanks @kmpaul

These are two issues. But the third one is that the original dataset ds is being modified inplace by ds.coarsen. This should never happen.

Also, while I was walking through the logic in this problem, I found that in the _reduce_method functions of the DataArrayCoarsen and DatasetCoarsen classes, the kwargs variable is being shadowed:

https://github.com/pydata/xarray/blob/df7b2eae3a26c1e86bd5f1dd7dab9cc8c4e53914/xarray/core/rolling.py#L692-L701

So, you can see that the skipna option is just being ignored. That's another pretty easy fix, but it will change existing behavior. It might be prudent to look to see if there are any known bug reports referencing the skipna parameter being ignored.

@dcherian @jukent: After a little walk through the code, I think the problem is in xarray/core/variable.py. If you look at the first part of the coarsen function in this file:

https://github.com/pydata/xarray/blob/df7b2eae3a26c1e86bd5f1dd7dab9cc8c4e53914/xarray/core/variable.py#L1945-L1953

you will see that **kwargs is not being pass into the _coarsen_reshape function:

https://github.com/pydata/xarray/blob/df7b2eae3a26c1e86bd5f1dd7dab9cc8c4e53914/xarray/core/variable.py#L1961

And down at the bottom of that function:

https://github.com/pydata/xarray/blob/df7b2eae3a26c1e86bd5f1dd7dab9cc8c4e53914/xarray/core/variable.py#L2024-L2025

it retrieves the keep_attrs parameter from global options, and doesn't check for a passed-in argument.

@jukent, why don't you draft a PR to fix this problem?

After some testing, I discovered that:

```python

Your code here

import xarray as xr

xr.set_options(keep_attrs=True) # NOTE GLOBAL OPTION!!!!

ds = xr.tutorial.load_dataset("air_temperature") ds2 = xr.tutorial.load_dataset("air_temperature")

xr.testing.assert_identical(ds, ds2) # passes ds.coarsen(lat=5).mean() xr.testing.assert_identical(ds, ds2) # passes ```

makes your example pass. So, it seems that somewhere along the chain of functions the keep_attrs parameter is being lost or modified.