Renaming an anonymous dimension

[ScottHosking]

Hi, I have loaded a cubelist but I am having issues merging the data into a single cube (see below).

Is there a way to force hist[2] to use 'time' as the first coordinate?

MergeError: failed to merge into a single cube.
  Coordinates in cube.dim_coords differ: time.
  Coordinate-to-dimension mapping differs for cube.dim_coords.
  Coordinates in cube.aux_coords (non-scalar) differ: season_year, clim_season, time.
  Coordinate-to-dimension mapping differs for cube.aux_coords (non-scalar).

In [219]: hist
Out[219]:
[<iris 'Cube' of northward_wind / (m s-1) (time: 4; latitude: 160; longitude: 320)>,
<iris 'Cube' of northward_wind / (m s-1) (time: 4; latitude: 160; longitude: 320)>,
<iris 'Cube' of northward_wind / (m s-1) (-- : 4; latitude: 160; longitude: 320)>,
<iris 'Cube' of northward_wind / (m s-1) (time: 4; latitude: 160; longitude: 320)>,
<iris 'Cube' of northward_wind / (m s-1) (time: 4; latitude: 160; longitude: 320)>]

Here is the output for `print hist[2]` and a cube without this issue (hist[1]).  I am not sure why 'time' has become an Auxiliary coordinate within hist[2]

In [220]: print hist[2]
northward_wind / (m s-1)            (-- : 4; latitude: 160; longitude: 320)
     Dimension coordinates:
          latitude                      -            x               -
          longitude                     -            -               x
     Auxiliary coordinates:
          clim_season                   x            -               -
          season_year                   x            -               -
          time                          x            -               -
     Scalar coordinates:
          RunID: r2i1p1
          air_pressure: 85000.0 Pa
     Cell methods:
          mean: time (30 minutes)
          mean: clim_season, season_year
          mean: clim_season

In [221]: print hist[1]
northward_wind / (m s-1)            (time: 4; latitude: 160; longitude: 320)
     Dimension coordinates:
          time                           x            -               -
          latitude                       -            x               -
          longitude                      -            -               x
     Auxiliary coordinates:
          clim_season                    x            -               -
          season_year                    x            -               -
     Scalar coordinates:
          RunID: r4i1p2
          air_pressure: 85000.0 Pa
     Cell methods:
          mean: time (30 minutes)
          mean: clim_season, season_year
          mean: clim_season

[Richard Hattersley]

Sounds like you might be interested in a recent pull-request: https://github.com/SciTools/iris/pull/1567 ?

Richard

[ScottHosking]

Thanks Richard, that's looks to be exactly what I'm looking for.

Is there a way I could make this change using a released version of Iris?  (1.7.3+)

[Richard Hattersley]

Fixing your misbehaving "time" coordinate(*) should just need:

old_time = hist[2].coord('time')
new_time = iris.coords.DimCoord.from_coord(old_time)
hist[2].remove_coord(old_time)
hist[2].add_dim_coord(new_time, 0)

*) The call to DimCoord.from_coord() will raise an error if the values are not suitable - i.e. numeric and monotonic.

Richard

[ScottHosking]

Thank you Richard,

Although, as you say, this raised the error "The points array must be strictly monotonic."