cumsum drops coordinate in Dataset but not DataArray

What happened?

Inconsistent behavior between cumulative sum on Dataset and DataArrray - Dataset.cumsum drops coordinate along reduction dim (even though cumsum is not actually a reduction).

DataArray does not do this. The dimension is still there, but as a dimension without a coordinate.

What did you expect to happen?

Expected Dataset to behave like DataArray, without dropping the coordinate.

Minimal Complete Verifiable Example

import xarray as xr

ds = xr.Dataset({"var1": (('dim1', ), [0, 1, 2])}, coords={"dim1": ['a', 'b', 'c']})
print(ds)

print("\n\nDataset cumsum:\n")
print(ds.cumsum(dim="dim1"))

print("\n\nDataArray cumsum:\n")
print(ds["var1"].cumsum(dim="dim1"))

MVCE confirmation

[X] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
[X] Complete example — the example is self-contained, including all data and the text of any traceback.
[X] Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
[X] New issue — a search of GitHub Issues suggests this is not a duplicate.
[X] Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

<xarray.Dataset> Size: 36B
Dimensions:  (dim1: 3)
Coordinates:
  * dim1     (dim1) <U1 12B 'a' 'b' 'c'
Data variables:
    var1     (dim1) int64 24B 0 1 2

Dataset cumsum:

<xarray.Dataset> Size: 24B
Dimensions:  (dim1: 3)
Dimensions without coordinates: dim1
Data variables:
    var1     (dim1) int64 24B 0 1 3

DataArray cumsum:

<xarray.DataArray 'var1' (dim1: 3)> Size: 24B
array([0, 1, 3])
Coordinates:
  * dim1     (dim1) <U1 12B 'a' 'b' 'c'

Anything else we need to know?

No response

Environment

INSTALLED VERSIONS ------------------ commit: None python: 3.11.4 | packaged by conda-forge | (main, Jun 10 2023, 18:08:41) [Clang 15.0.7 ] python-bits: 64 OS: Darwin OS-release: 24.0.0 machine: arm64 processor: arm byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: ('en_US', 'UTF-8') libhdf5: 1.14.0 libnetcdf: 4.9.2 xarray: 2024.10.0 pandas: 2.2.3 numpy: 1.24.3 scipy: 1.14.1 netCDF4: 1.6.4 pydap: None h5netcdf: None h5py: 3.8.0 zarr: 2.18.3 cftime: 1.6.2 nc_time_axis: None iris: None bottleneck: 1.3.7 dask: 2024.8.0 distributed: 2024.8.0 matplotlib: 3.7.1 cartopy: 0.24.0 seaborn: 0.12.2 numbagg: None fsspec: 2023.6.0 cupy: None pint: None sparse: None flox: 9.11 numpy_groupies: 0.11.2 setuptools: 67.7.2 pip: 23.1.2 conda: None pytest: None mypy: None IPython: 8.14.0 sphinx: None

pydata / xarray