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/443#issuecomment-115933651,https://api.github.com/repos/pydata/xarray/issues/443,115933651,MDEyOklzc3VlQ29tbWVudDExNTkzMzY1MQ==,1217238,2015-06-27T01:22:25Z,2015-06-27T22:44:02Z,MEMBER,"OK, I understand now. One of these files looks like:

```
<xray.Dataset>
Dimensions:            (lat: 39, lon: 59, mean_height_agl: 50, time: 1)
Coordinates:
  * time               (time) datetime64[ns] 2011-05-21T13:00:00
  * lon                (lon) float64 -29.0 -28.0 -27.0 -26.0 -25.0 -24.0 ...
  * lat                (lat) float64 32.0 33.0 34.0 35.0 36.0 37.0 38.0 39.0 ...
  * mean_height_agl    (mean_height_agl) float64 28.28 97.21 191.1 310.7 ...
Data variables:
    ash_concentration  (mean_height_agl, lat, lon) float64 9.583e-16 ...
    ash_mass_loading   (lat, lon) float64 1.091e-11 1.091e-11 1.091e-11 ...
    ash_drydep         (lat, lon) float64 4.086e-10 4.084e-10 4.08e-10 ...
    ash_wetdep         (lat, lon) float64 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ...
    so2_concentration  (mean_height_agl, lat, lon) float64 3.199e-13 ...
    so2_mass_loading   (lat, lon) float64 2.602e-09 2.602e-09 2.602e-09 ...
```

The problem is that the `mean_height_agl` coordinate changes between each file.

Another interesting aspect of this file, which relates to how I as hoping to fix https://github.com/xray/xray/issues/438, is that it includes a time coordinate with length 1, but none of the other dataset variables use that coordinate.

This suggests to me that we need some sort of hook that can allow you to transform a single dataset _before_ they are joined with `open_mfdataset`. Perhaps a `preprocess` argument? Then you could write, e.g.,:

``` python
def fix_my_data(ds):
    return (ds.assign_coords(
                agl=('mean_height_agl', range(ds.dims['mean_height_agl'])))
            .swap_dims({'mean_height_agl': 'agl'})
            .squeeze('time'))

ds = xray.open_mfdataset('*.nc', preprocess=fix_my_data)
```
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,91109966
https://github.com/pydata/xarray/issues/443#issuecomment-115903258,https://api.github.com/repos/pydata/xarray/issues/443,115903258,MDEyOklzc3VlQ29tbWVudDExNTkwMzI1OA==,1217238,2015-06-26T22:02:50Z,2015-06-26T22:02:50Z,MEMBER,"Do you concatenate these files along one of the existing axes or a new axis? This might require new API but should probably be supported.

Could you print two of these netCDF files that you want to automatically combine with `open_mfdataset`? I know they have the same structure but it's useful to see how/if the values differ.
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,91109966
https://github.com/pydata/xarray/issues/443#issuecomment-115887945,https://api.github.com/repos/pydata/xarray/issues/443,115887945,MDEyOklzc3VlQ29tbWVudDExNTg4Nzk0NQ==,1217238,2015-06-26T21:26:19Z,2015-06-26T21:26:19Z,MEMBER,"Marking this as a bug, I'll see if I can reproduce this with a similar dataset.
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,91109966
https://github.com/pydata/xarray/issues/443#issuecomment-115492420,https://api.github.com/repos/pydata/xarray/issues/443,115492420,MDEyOklzc3VlQ29tbWVudDExNTQ5MjQyMA==,1217238,2015-06-26T03:48:08Z,2015-06-26T03:48:08Z,MEMBER,"Do you get the error message if you specify the full path to this file in open_mfdataset?
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,91109966
https://github.com/pydata/xarray/issues/443#issuecomment-115449452,https://api.github.com/repos/pydata/xarray/issues/443,115449452,MDEyOklzc3VlQ29tbWVudDExNTQ0OTQ1Mg==,1217238,2015-06-26T01:01:45Z,2015-06-26T01:01:45Z,MEMBER,"Could you print two of the incompatible datasets? I'm not sure if there is a general pattern here (or not).
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,91109966