issues: 1468838643

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
1468838643 I_kwDOAMm_X85XjLLz 7336 Instability when calculating standard deviation 26401994 closed 0     4 2022-11-29T23:33:55Z 2023-03-10T20:32:51Z 2023-03-10T20:32:50Z NONE      

What happened?

I noticed that for some large values (not really that large) and lots of samples, the data.std() yields different values than np.std(data). This seems to be related to the magnitude. See attached code here: nino34_tas_picontrol_detrend = nino34_tas_picontrol-298 std_dev = nino34_tas_picontrol_detrend.std() print(std_dev.data) std_dev = nino34_tas_picontrol.std() print(std_dev.data) nino34_tas_picontrol_detrend = nino34_tas_picontrol-10 std_dev = nino34_tas_picontrol_detrend.std() print(std_dev.data) and the results are: 1.4448999166488647 24.911161422729492 20.054718017578125

So I guess this is related to the magnitude, but not sure. Anyone has similar issue?

What did you expect to happen?

Adding or subtracting a constant should not change the standard deviation. See screenshot here about what the data look like:

Minimal Complete Verifiable Example

No response

MVCE confirmation

  • [ ] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
  • [ ] Complete example — the example is self-contained, including all data and the text of any traceback.
  • [ ] Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
  • [ ] New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

No response

Anything else we need to know?

No response

Environment

INSTALLED VERSIONS ------------------ commit: None python: 3.10.4 (main, Mar 31 2022, 08:41:55) [GCC 7.5.0] python-bits: 64 OS: Linux OS-release: 3.10.0-1160.71.1.el7.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: ('en_US', 'UTF-8') libhdf5: 1.12.2 libnetcdf: 4.8.1 xarray: 2022.6.0 pandas: 1.4.4 numpy: 1.22.3 scipy: 1.8.1 netCDF4: 1.6.1 pydap: None h5netcdf: None h5py: None Nio: None zarr: None cftime: 1.6.2 nc_time_axis: 1.4.1 PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: 1.3.5 dask: 2022.9.0 distributed: 2022.9.0 matplotlib: 3.5.2 cartopy: 0.21.0 seaborn: None numbagg: None fsspec: 2022.10.0 cupy: None pint: None sparse: 0.13.0 flox: None numpy_groupies: None setuptools: 65.5.0 pip: 22.2.2 conda: None pytest: None IPython: 8.6.0 sphinx: None 
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   completed 13221727 issue

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