issues: 117478779

I have had some problem with some dataset I have created by slicing from an existing dataset. Some operations I’m trying to perform on that new dataset fail because it doesn't pass some checking that goes on in xray.core.variable.py (Variable._parse_dimensions()).

This is the original dataset:

<xray.Dataset> Dimensions: (depth: 40, lat: 2001, lon: 4500, time: 1) Coordinates: * time (time) float64 3.502e+04 * depth (depth) float64 0.0 2.0 4.0 6.0 8.0 10.0 12.0 15.0 20.0 25.0 ... * lat (lat) float64 -80.0 -79.92 -79.84 -79.76 -79.68 -79.6 -79.52 ... * lon (lon) float64 -180.0 -179.9 -179.8 -179.8 -179.7 -179.6 ... Data variables: tau (time) float64 0.0 water_u (time, depth, lat, lon) float64 nan nan nan nan nan nan nan ... water_v (time, depth, lat, lon) float64 nan nan nan nan nan nan nan ... water_temp (time, depth, lat, lon) float64 nan nan nan nan nan nan nan ... salinity (time, depth, lat, lon) float64 nan nan nan nan nan nan nan ... surf_el (time, lat, lon) float64 nan nan nan nan nan nan nan nan nan ... Attributes: classification_level: UNCLASSIFIED distribution_statement: Approved for public release. Distribution unlimited. downgrade_date: not applicable classification_authority: not applicable institution: Naval Oceanographic Office source: HYCOM archive file history: archv2ncdf3z field_type: instantaneous Conventions: CF-1.0 NAVO_netcdf_v1.0

This is how I have sliced it to create my new dataset,

dset_new = dset['water_u'].sel(lat=[-30], depth=[0, 10, 20], lon=[0], method='nearest').to_dataset(name='water_u')

And this is how the new dataset looks like:

<xray.Dataset> Dimensions: (depth: 3, lat: 1, lon: 1, time: 1) Coordinates: * lat (lat) float64 -30.0 * depth (depth) float64 0.0 10.0 20.0 * lon (lon) float64 0.0 * time (time) float64 3.502e+04 Data variables: water_u (time, depth, lat, lon) float64 0.104 0.138 0.144

This only has one variable, but in my case I also add some others. I could not identify anything obviously wrong with this new dataset.

I was trying to concatenate similar datasets sliced from multiple files. But the same error happens if for example I try to dump it as a netcdf using to_netcdf(). This is the most recent call of the Traceback:

``` /usr/lib/python2.7/site-packages/xray-0.6.1_15_g5109f4f-py2.7.egg/xray/core/variable.py in _parse_dimensions(self, dims) 302 raise ValueError('dimensions %s must have the same length as the ' 303 'number of data dimensions, ndim=%s' --> 304 % (dims, self.ndim)) 305 return dims 306

ValueError: dimensions (u'time', u'depth', u'lat', u'lon') must have the same length as the number of data dimensions, ndim=2 ```

I’m not sure what the “number of data dimensions” ndim represents, but my new dataset is not passing that check (len(dims)==4 but self.ndim==2). However if I comment out that check, everything works - I can concatenate datasets, and dump them to netcdf files.

Thanks, Rafael