html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/7076#issuecomment-1431400086,https://api.github.com/repos/pydata/xarray/issues/7076,1431400086,IC_kwDOAMm_X85VUW6W,18679148,2023-02-15T13:49:45Z,2023-02-16T13:43:29Z,NONE,"Hi @DWesl, @benbovy 

I got a bug very similar to what was initially report with the following minimal example (xarray version 2022.11.0) with the error:
> ValueError: cannot unstack dimensions that do not have exactly one multi-index: ('z',)

It is working fine with my previous version (xarray 0.16.0)
```python
import xarray as xr
ds = xr.Dataset(
    data_vars=dict(
        mydata = ( ['across', 'along'], [[0,1],[2,3]])
    )
)
stacked = ds.stack(z=(""across"", ""along""))
newlist = [None] * stacked.z.size
for ii, zindex in enumerate(stacked.z.data):
    newlist[ii] = stacked.mydata.sel(z=zindex)
newds = xr.concat(newlist, dim='z')
newds['z'] = stacked.z
print('xarray version:' + xr.__version__)
newds.unstack(dim='z')
```

If I do `newds = newds.reset_index('z')` just before the last line, it is solved for my minimal example. But it still doesn't work for my real problem and I don't think it is the best way to proceed.

Many thanks for your help,
Adrien




","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1384465119
https://github.com/pydata/xarray/issues/7076#issuecomment-1433104955,https://api.github.com/repos/pydata/xarray/issues/7076,1433104955,IC_kwDOAMm_X85Va3I7,18679148,2023-02-16T13:41:12Z,2023-02-16T13:41:12Z,NONE,"> 

Hi @benbovy, my code works for 2 dimensions, but it doesn't with 1D. I think the error comes from `.set_index(z=['across'])` which delivers a ""PandasIndex(Int64Index("" and not the expected ""PandasIndex(MultiIndex("" for `unstack`.

I created a Pandas-MultiIndex ""MultiIndex([((0,), (1,))], names=['z', 'across'])"" (see code just below), but it is not exactly the same one as the one created by `.stack()` ""PandasIndex(MultiIndex([(0,),(1,)], name='z'))"" and I didn't find out how to pass the 'index' to xarray.
```python
import pandas as pd
tuples = [(0,),(1,)],
index = pd.MultiIndex.from_tuples(tuples, names=[""z"",""across""])
index
```

My modified minimal example is as below:
```python
import xarray as xr
ds = xr.Dataset(
    data_vars=dict(
        mydata = ( ['across', 'along'], [[0,1],[2,3]])
    ),
    coords=dict( # <- changed 
        across=[0,1], # <- changed 
        along=[0,1], # <- changed 
    ),    # <- changed
)
stacked = ds.isel(along=0).stack(z=[""across""]) # <- changed
newlist = [None] * stacked.z.size
for ii, zindex in enumerate(stacked.z.data):
    newlist[ii] = stacked.mydata.sel(z=zindex)
newds = xr.concat(newlist, dim='z')
newds = newds.set_index(z=['across']) # <- changed
newds.unstack(dim='z') # Fail with ValueError: cannot unstack dimensions that do not have exactly one multi-index: ('z',)
```



","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1384465119
https://github.com/pydata/xarray/issues/7076#issuecomment-1431736710,https://api.github.com/repos/pydata/xarray/issues/7076,1431736710,IC_kwDOAMm_X85VVpGG,18679148,2023-02-15T17:24:27Z,2023-02-15T17:24:27Z,NONE,"> Many thanks for the explanation and the rapid answer. I am not very familiar with multi-index.
> 
> My real problem works with a DataSet with different sort of variables:
> 
> ```
> ipdb> lmmap
> <xarray.Dataset>
> Dimensions:        (x_variables: 4, Observables: 2, Antenna: 4, z: 4,
>                     Ambiguities: 4, fun_variables: 8, extrema: 2)
> Coordinates:
>   * x_variables    (x_variables) <U3 'u' 'v' 'c_u' 'c_v'
>   * Observables    (Observables) <U6 'sigma0' 'RVL'
>   * Antenna        (Antenna) <U4 'Fore' 'MidV' 'MidH' 'Aft'
>     fun_variables  (Observables, Antenna) int64 0 1 2 3 4 5 6 7
> Dimensions without coordinates: z, Ambiguities, extrema
> Data variables: (12/17)
>     x              (z, Ambiguities, x_variables) float64 -4.503 7.8 ... -0.4265
>     active_mask    (z, Ambiguities, x_variables) int64 0 0 0 0 0 0 ... 0 0 0 0 0
>     grad           (z, Ambiguities, x_variables) float64 7.816e-11 ... -1.873...
>     fun            (z, Ambiguities, Observables, Antenna) float64 0.001137 .....
>     jac            (z, Ambiguities, fun_variables, x_variables) float64 0.359...
>     x0             (z, Ambiguities, x_variables) float64 -7.002 10.03 ... 1.219
>     ...             ...
>     message        (z, Ambiguities) <U42 '`xtol` termination condition is sat...
>     success        (z, Ambiguities) bool True True True True ... True True True
>     method         (z) <U3 'trf' 'trf' 'trf' 'trf'
>     xtol           (z) float64 0.001 0.001 0.001 0.001
>     x_scale        (z, x_variables) float64 7.0 7.0 0.5 0.5 ... 7.0 7.0 0.5 0.5
>     bounds         (z, extrema, x_variables) int64 -30 -30 -5 -5 ... 30 30 5 5
> ```
> 
> I don't know where I should apply `set_index(z=[""across"", ""along""])` I tried on the full DataSet or a single DataArray but without success. I get the following error:
> 
> > ValueError: across, along variable(s) do not exist
> 
> Which is obvious as across and along variables disappeared. Thank you, I will dig in this direction why it happens.
> 
> However, it works perfectly with the minimal example. Many thanks

Thanks @benbovy, my issue is now resolved, once I have enabled the coords to follow.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1384465119
https://github.com/pydata/xarray/issues/7076#issuecomment-1431676036,https://api.github.com/repos/pydata/xarray/issues/7076,1431676036,IC_kwDOAMm_X85VVaSE,18679148,2023-02-15T16:51:49Z,2023-02-15T16:51:49Z,NONE,I didn't see any warning for this,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1384465119
https://github.com/pydata/xarray/issues/7076#issuecomment-1431645539,https://api.github.com/repos/pydata/xarray/issues/7076,1431645539,IC_kwDOAMm_X85VVS1j,2448579,2023-02-15T16:30:21Z,2023-02-15T16:30:21Z,MEMBER,"> the issue is when you do newds['z'] = stacked.z

Are we raising a warning here?","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1384465119
https://github.com/pydata/xarray/issues/7076#issuecomment-1431529928,https://api.github.com/repos/pydata/xarray/issues/7076,1431529928,IC_kwDOAMm_X85VU2nI,18679148,2023-02-15T15:15:23Z,2023-02-15T15:20:58Z,NONE,"Many thanks for the explanation and the rapid answer. I am not very familiar with multi-index.

My real problem works with a DataSet with different sort of variables:

```
ipdb> lmmap
<xarray.Dataset>
Dimensions:        (x_variables: 4, Observables: 2, Antenna: 4, z: 4,
                    Ambiguities: 4, fun_variables: 8, extrema: 2)
Coordinates:
  * x_variables    (x_variables) <U3 'u' 'v' 'c_u' 'c_v'
  * Observables    (Observables) <U6 'sigma0' 'RVL'
  * Antenna        (Antenna) <U4 'Fore' 'MidV' 'MidH' 'Aft'
    fun_variables  (Observables, Antenna) int64 0 1 2 3 4 5 6 7
Dimensions without coordinates: z, Ambiguities, extrema
Data variables: (12/17)
    x              (z, Ambiguities, x_variables) float64 -4.503 7.8 ... -0.4265
    active_mask    (z, Ambiguities, x_variables) int64 0 0 0 0 0 0 ... 0 0 0 0 0
    grad           (z, Ambiguities, x_variables) float64 7.816e-11 ... -1.873...
    fun            (z, Ambiguities, Observables, Antenna) float64 0.001137 .....
    jac            (z, Ambiguities, fun_variables, x_variables) float64 0.359...
    x0             (z, Ambiguities, x_variables) float64 -7.002 10.03 ... 1.219
    ...             ...
    message        (z, Ambiguities) <U42 '`xtol` termination condition is sat...
    success        (z, Ambiguities) bool True True True True ... True True True
    method         (z) <U3 'trf' 'trf' 'trf' 'trf'
    xtol           (z) float64 0.001 0.001 0.001 0.001
    x_scale        (z, x_variables) float64 7.0 7.0 0.5 0.5 ... 7.0 7.0 0.5 0.5
    bounds         (z, extrema, x_variables) int64 -30 -30 -5 -5 ... 30 30 5 5
```

I don't know where I should apply `set_index(z=[""across"", ""along""])` I tried on the full DataSet or a single DataArray but without success. I get the following error:

> ValueError: across, along variable(s) do not exist

Which is obvious as across and along variables disappeared. Thank you, I will dig in this direction why it happens.

However, it works perfectly with the minimal example.
Many thanks

","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1384465119
https://github.com/pydata/xarray/issues/7076#issuecomment-1431496828,https://api.github.com/repos/pydata/xarray/issues/7076,1431496828,IC_kwDOAMm_X85VUuh8,4160723,2023-02-15T14:54:27Z,2023-02-15T14:54:27Z,MEMBER,"@ACHMartin the issue is when you do `newds['z'] = stacked.z`. In the last versions of Xarray multi-index levels have each their own (real) coordinates, for consistency and clarity we soon won't support assigning a multi-index to a single coordinate of a Dataset / DataArray like that.

I think that in other places we still do support it with a deprecation notice, but apparently in your example this is not the case. `unstack` doesn't work because the multi-index(es) and the coordinates of `newds` are not consistent.

I don't know exactly what is your real problem, but from now on you should avoid implicitly assign a multi-index with `xr_obj[""my_coord""] = ...` or `xr_obj.assign(my_coord=...)`. Instead you should re-create the multi-index, e.g., in your minimal example `newds = newds.set_index(z=[""across"", ""along""])`.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1384465119
https://github.com/pydata/xarray/issues/7076#issuecomment-1259894192,https://api.github.com/repos/pydata/xarray/issues/7076,1259894192,IC_kwDOAMm_X85LGHWw,22566757,2022-09-27T18:28:26Z,2022-09-27T18:28:26Z,CONTRIBUTOR,"Fix confirmed, thank you.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1384465119
https://github.com/pydata/xarray/issues/7076#issuecomment-1257965977,https://api.github.com/repos/pydata/xarray/issues/7076,1257965977,IC_kwDOAMm_X85K-wmZ,4160723,2022-09-26T12:32:59Z,2022-09-26T12:32:59Z,MEMBER,"Hi @DWesl,

Your example is working with the `main` branch, it has been fixed in #6889.

```python
# after #6889
arr2.unstack(""index0"")
# <xarray.DataArray (index2: 2, level_0: 3, level_1: 5)>
# array([[[ 0,  1,  2,  3,  4],
#         [ 5,  6,  7,  8,  9],
#         [10, 11, 12, 13, 14]],
# 
#        [[ 0,  1,  2,  3,  4],
#         [ 5,  6,  7,  8,  9],
#         [10, 11, 12, 13, 14]]])
# Coordinates:
#   * level_0  (level_0) int64 0 1 2
#   * level_1  (level_1) int64 0 1 2 3 4
# Dimensions without coordinates: index2
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,1384465119