Xarray: slicing latitude longitude using dimension name

Question

I am writing a program that will open Meteorological NetCDF data, slice it for a given region and then do some calculations, for example:

data =xr.open_dataset(SomeFile)

SlicedData = data.sel(lat=slice(max_lat,min_lat),
                lon=slice(min_lon,max_lon))
ExampleResult = SlicedData.mslp.average('lon')

Here follows an example of how ‘data’ might be scrtuctured:

<xarray.Dataset>
Dimensions:  (lon: 144, lat: 37, level: 17, time: 25)
Coordinates:
  * lon      (lon) float32 -180.0 -177.5 -175.0 -172.5 ... 172.5 175.0 177.5
  * lat      (lat) float32 0.0 -2.5 -5.0 -7.5 -10.0 ... -82.5 -85.0 -87.5 -90.0
  * level    (level) float32 1e+03 925.0 850.0 700.0 ... 50.0 30.0 20.0 10.0
  * time     (time) datetime64[ns] 2011-05-25 2011-05-25T06:00:00 ... 2011-05-31
Data variables:
    air      (time, level, lat, lon) float32 ...
    hgt      (time, level, lat, lon) float32 ...
    rhum     (time, level, lat, lon) float32 ...
    omega    (time, level, lat, lon) float32 ...
    uwnd     (time, level, lat, lon) float32 ...
    vwnd     (time, level, lat, lon) float32 ...
    mslp     (time, lat, lon) float32 ...

However, distinct data sources store the latitude and longitude coordinates using different indexers: it could be, for example, either latitude/longitude or lat/lon. So, for example, if the indexers used are latitude/longitude, the following:

SlicedData = data.sel(lat=slice(max_lat,min_lat),
                    lon=slice(min_lon,max_lon))

Would return:

KeyError: 'lat is not a valid dimension or coordinate'

Is there a way I can slice the data using Xarray using a string for the coordinate indexer? For example:

LatIndexer, LonIndexer = 'lat', 'lon'
SlicedData = data.sel(LatIndexer=slice(max_lat,min_lat),
                        LonIndexer=slice(min_lon,max_lon))

Asked By: daniloceano

||

Source

Answer 1

Just pass by dictionary:

LatIndexer, LonIndexer = 'lat', 'lon'
SliceData = data.sel(**{LatIndexer: slice(max_lat, min_lat),
                        LonIndexer: slice(max_lon, min_lon)})

Alternatively

LatIndexer, LonIndexer = 'lat', 'lon'
SliceData = data.loc[{LatIndexer: slice(max_lat, min_lat),
                      LonIndexer: slice(max_lon, min_lon)}]

Reference Indexing and selecting data

Answered By: MYousefi

Answer 2

I do not understand why the slice elements for lat and long in the question are given in inverse format..

SlicedData = data.sel(lat=slice(max_lat,min_lat),
            lon=slice(min_lon,max_lon))

Any explanation?

Answered By: mn5hk

Xarray: slicing latitude longitude using dimension name

Question:

Answers: