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
1363366455,I_kwDOAMm_X85RQ1I3,6997,`ffill` does not spread chunks when used with dask.array,17484729,closed,0,,,5,2022-09-06T14:20:29Z,2022-09-08T15:42:57Z,2022-09-08T15:42:57Z,NONE,,,,"### What is your issue?

When using xarray with dask.array as in the following example:
```
import numpy as np
import xarray as xr
import dask
ds_ = xr.Dataset()
ds_[""test""] = (""dim_0"",), dask.array.from_array(
    [0, 1, np.nan, np.nan, np.nan], chunks=2
)
```
then the `ffill` method does not seem to propagate through the underlying chunks used by dask.array.
In the example above, this means that
```
 ds_.ffill(""dim_0"").compute().test.values
```
gives
```
>>> array([ 0., 1., 1., 1., nan])
```
where 
```
ds_.compute().ffill(""dim_0"").test.values
```
gives
```
>>> array([0., 1., 1., 1., 1., 1.])
```

Is it an expected behavior ?","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/6997/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue