How can I reverse Coordinate vector and apply transformation to all Data Variables?

Andrew Joros

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Nov 7, 2016, 6:48:20 AM11/7/16

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Hi all,

I have tried googling around without luck, and maybe it's because I'm not sure what proper keywords to enter, but here is my question:

I have the following Dataset in xarray (see below). I am looking to flip the "latitude" coordinate and consequently apply it to all the Data Variables. Naturally, latitude should go from largest to smallest value (90 to -90), and when I tried to use something like latitude[::-1], it doesn't apply that reversing function to the data variables themselves. I tested this by grabbing the value from TMP_2maboveground[0,50,50] before and after reversing the latitude vector. The values came back the same which can't be possible since they should be two different locations on Earth before and after reversing latitude vector.

In short, how can I reverse the latitude vector and apply it to all the Data Variables?

<xarray.Dataset> Dimensions: (latitude: 721, longitude: 1440, time: 1) Coordinates: * latitude (latitude) float64 -90.0 -89.75 -89.5 -89.25 -89.0 ... * longitude (longitude) float64 0.0 0.25 0.5 0.75 1.0 1.25 1.5 ... * time (time) datetime64[ns] 2016-11-10T12:00:00 Data variables: TMP_2maboveground (time, latitude, longitude) float64 234.9 234.9 ... RH_2maboveground (time, latitude, longitude) float64 96.8 96.8 96.8 ... TMAX_2maboveground (time, latitude, longitude) float64 234.9 234.9 ... TMIN_2maboveground (time, latitude, longitude) float64 234.3 234.3 ... UGRD_10maboveground (time, latitude, longitude) float64 -1.17 -1.16 ... VGRD_10maboveground (time, latitude, longitude) float64 -4.26 -4.27 ... PRATE_surface (time, latitude, longitude) float64 1e-06 1e-06 ... DSWRF_surface (time, latitude, longitude) float64 310.0 310.0 ... PRMSL_meansealevel (time, latitude, longitude) float64 1.024e+05 ... Attributes: Conventions: COARDS History: created by wgrib2 GRIB2_grid_template: 0

Thanks

Andy

Stephan Hoyer

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Nov 7, 2016, 11:31:59 AM11/7/16

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I think ds.sel(latitude=slice(None, None -1)) should do the trick -- it will reverse the latitude axis on every variable.

Side note: StackOverflow is even better than the mailing list for questions like this, because it turns up better in search.

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Andrew Joros

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Nov 7, 2016, 3:14:22 PM11/7/16

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Hmmm, it's not liking your hyphen in "None-1". TypeError: unsupported operand type(s) for -: 'NoneType' and 'int'

I will attempt to duplicate and post on StackOverflow as well.

Thanks Stephan

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erol512

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Nov 7, 2016, 3:22:50 PM11/7/16

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Hi Andrew,

I believe Stephan meant to write ds.sel(latitude=slice(None, None, ::-1)). This should work.

Cheers,

Jeremy

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Andrew Joros

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Nov 7, 2016, 3:27:30 PM11/7/16

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Unfortunately, that's returning "invalid syntax" as I think slice only takes 2 arguments, not 3 like you posted.

  File "<ipython-input-100-86b2cfc60863>", line 1
    tempDS.sel(lat=slice(None, None, ::-1))
                                     ^
SyntaxError: invalid syntax

Stephan Hoyer

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Nov 7, 2016, 3:38:08 PM11/7/16

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I was missing a comma:

ds.sel(latitude=slice(None, None, -1))

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