Unable to run groupby, map after shuffle_to_chunks

[joshua-gould]

What happened?

ValueError: Array chunk size or shape is unknown. Possible solution with x.compute_chunk_sizes()

What did you expect to happen?

Able to successfully iterate over groups and apply a function

Minimal Complete Verifiable Example

# /// script
# requires-python = ">=3.11"
# dependencies = [
#   "xarray[complete]@git+https://github.com/pydata/xarray.git@main",
# ]
# ///
#
# This script automatically imports the development branch of xarray to check for issues.
# Please delete this header if you have _not_ tested this script with `uv run`!

import xarray as xr
xr.show_versions()
import dask.array as da
import numpy as np
import xarray as xr

data = da.ones((583753, 184), chunks=(18243, 12))

y = np.random.choice(np.array([1, 2, 3, 4, 5]), size=data.shape[0], replace=True)
d = xr.DataArray(data=data, coords={"y": y}, dims=["y", "x"])
d = d.groupby("y").shuffle_to_chunks()
d.data = d.data.compute_chunk_sizes()
d.groupby("y").map(lambda x: x)[
    0, 0].compute()  # ValueError: Array chunk size or shape is unknown. Possible solution with x.compute_chunk_sizes()

Steps to reproduce

No response

MVCE confirmation

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

Relevant log output

Anything else we need to know?

No response

Environment

Details

INSTALLED VERSIONS

commit: None
python: 3.12.12 | packaged by conda-forge | (main, Jan 27 2026, 00:01:15) [Clang 19.1.7 ]
python-bits: 64
OS: Darwin
OS-release: 25.3.0
machine: arm64
processor: arm
byteorder: little
LC_ALL: None
LANG: C.UTF-8
LOCALE: ('C', 'UTF-8')
libhdf5: 1.14.6
libnetcdf: None
xarray: 2026.2.0
pandas: 2.3.3
numpy: 1.26.4
scipy: 1.16.3
netCDF4: None
pydap: None
h5netcdf: 1.8.1
h5py: 3.15.1
zarr: 2.18.7
cftime: None
nc_time_axis: None
iris: None
bottleneck: None
dask: 2025.11.0
distributed: 2025.11.0
matplotlib: 3.10.8
cartopy: None
seaborn: 0.13.2
numbagg: None
fsspec: 2026.2.0
cupy: None
pint: 0.25.2
sparse: None
flox: 0.11.2
numpy_groupies: 0.11.3
setuptools: 82.0.0
pip: 26.0.1
conda: None
pytest: 9.0.2
mypy: None
IPython: 9.10.0
sphinx: None