Modifying Coordinate Variables

[erol512]

This seems like it should be a simple operation. Does someone know the proper way to modify a coordinate variable in a dataset that is being used as an index? I have a dataset with an invalid vertical axis that I want to correct and re-save.

Cheers,

Jeremy

[Stephan Hoyer]

With an index, coordinate values are immutable because they are backed by a pandas.Index (which has immutable values).

So it's most straightforward to replace a coordinate variable wholesale with something else, e.g.,

In [31]: ds = xr.Dataset(coords={'x': range(3)})

In [32]: ds['x'] = [5, 6, 7]

In [33]: ds

Out[33]:

<xarray.Dataset>

Dimensions:  (x: 3)

Coordinates:

  * x        (x) int64 5 6 7

Data variables:

    *empty*

In [36]: ds['x'] = 2 * ds['x']

In [37]: ds

Out[37]:

<xarray.Dataset>

Dimensions:  (x: 3)

Coordinates:

  * x        (x) float64 10.0 12.0 14.0

Data variables:

    *empty*

You can modify values with indexing if you convert to an ndarray and then reconstruct the coordinate. In principle, it should also work to modify a copy of a DataArray created from an index (e.g., ds['x'].copy()), but currently that remains immutable:

https://github.com/pydata/xarray/issues/954

--
You received this message because you are subscribed to the Google Groups "xarray" group.
To unsubscribe from this group and stop receiving emails from it, send an email to xarray+unsubscribe@googlegroups.com.
To post to this group, send email to xar...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/xarray/CAOTezYV5EuLg-jJvrDvH2QLyvCnY6bvsPSBhJ8kv0fdL8jRBVQ%40mail.gmail.com.
For more options, visit https://groups.google.com/d/optout.

[erol512]

Thanks! I was missing the fact that you could replace coordinate variables by assignment.

Jeremy

To view this discussion on the web visit https://groups.google.com/d/msgid/xarray/CAEQ_TvduYzwNs5n31SHwPWbZ%2BNMzxxSfBsd6m-qJfx5kYFK01g%40mail.gmail.com.