issues: 859611240

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
859611240 MDU6SXNzdWU4NTk2MTEyNDA= 5169 nan length coordinates 1053153 open 0     2 2021-04-16T08:50:50Z 2021-04-24T02:43:35Z   CONTRIBUTOR      

Is your feature request related to a problem? Please describe.

When using arrays with a nan shape, I'd like to provide a coordinate specification from a delayed object, which is my responsibility to make sure has the right chunks and length.

Describe the solution you'd like

Below are three examples that I think should work, where I give a coordinate via a dask array, a dask series, and a dask index. Currently, all three examples error out by computing the coordinate length (triggering an unwanted dask computation!), and then indicating that its different than the array's corresponding length, which is nan.

```python import dask import dask.array as da import dask.dataframe as dd import numpy as np import pandas as pd import xarray as xr

def foo(): return np.arange(4)

arr = da.from_delayed(dask.delayed(foo)(), shape=(np.nan,), dtype=int)

idx = da.from_delayed(dask.delayed(foo)(), shape=(np.nan,), dtype=int)

ddf = dd.from_pandas(pd.DataFrame({'y': np.arange(4)}), npartitions=1)

arr0 = xr.DataArray(arr, coords=[('z', idx)]) arr1 = xr.DataArray(arr, coords=[('z', ddf['y'])]) arr2 = xr.DataArray(arr, coords=[('z', ddf.index)]) ```

Error:

ValueError: conflicting sizes for dimension 'z': length nan on the data but length 4 on coordinate 'z'

Describe alternatives you've considered

After computations to complete add the missing coordinate. This requires carrying around the delayed index with the delayed array.

 
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     13221727 issue

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