Add RMS iris analysis operator to statistics preprocessor functions

[pepcos]

Adding RMS iris analysis operator (which allow Area Weighting) to the preprocessor. This allows computing root mean squares in the _area.py and _time.py preprocessors.

Tasks

• Create an issue to discuss what you are going to do, if you haven't done so already (and add the link at the bottom)
• This pull request has a descriptive title that can be used in a changelog
• Add unit tests
• If writing a new/modified preprocessor function, please update the documentation
• Circle/CI tests pass. Status can be seen below your pull request. If the tests are failing, click the link to find out why.
• Codacy code quality checks pass. Status can be seen below your pull request. If there is an error, click the link to find out why. If you suspect Codacy may be wrong, please ask by commenting.

---

closes #739

[bouweandela]

Thanks for the pull request! Could you please have a look at the failing test on CircleCI? Just click the commit link below, it looks like there is something wrong with the formatting of one of the docstrings. You can build the documentation on your own computer by following these instructions: https://docs.esmvaltool.org/projects/esmvalcore/en/latest/contributing.html#how-to-build-the-documentation-locally

[bouweandela]

Would you also be able to add some unit tests, e.g. similar to:

ESMValCore/tests/unit/preprocessor/_time/test_time.py

Lines 364 to 373 in 8e41213

	def test_time_median(self):
	"""Test for time meadian of a 1D field."""
	data = np.arange((3))
	times = np.array([15., 45., 75.])
	bounds = np.array([[0., 30.], [30., 60.], [60., 90.]])
	cube = self._create_cube(data, times, bounds)
	result = climate_statistics(cube, operator='median')
	expected = np.array([1.])
	assert_array_equal(result.data, expected)

and

ESMValCore/tests/unit/preprocessor/_area/test_area.py

Lines 79 to 83 in 8e41213

	def test_area_statistics_median(self):
	"""Test for area average of a 2D field."""
	result = area_statistics(self.grid, 'median')
	expected = np.array([1.])
	self.assert_array_equal(result.data, expected)

?

[pepcos]

Hi @bouweandela

I've never done unit testing so correct me if I'm wrong: Should I add a couple of functions to test_area.py and test_time.py in order to check that rms works fine?

Thanks!

[bouweandela]

Yes, that's the idea. You can just copy/paste the code of the examples mentioned above, replace 'median' by 'rms' and make sure the expected numbers match the computed result. To run the tests in a particular file, you can run pytest tests/unit/preprocessor/_time/test_time.py, see also https://docs.pytest.org

[bouweandela]

Thanks! Could you please carefully check that you update the documentation for all preprocessor functions? It looks like you missed a few: 'rms' is missing at least in timeseries_filter, and in preprocessor.rst: zonal_statistics and meridional_statistics.

[pepcos]

Thanks for checking @bouweandela !

@sloosvel coould you have a look at it? Thanks.

[sloosvel]

Looks fine to me, good job @pcosbsc .

[bouweandela]

@mattiarighi or @valeriupredoi Could you please test?

[bouweandela]

@sloosvel or @jvegasbsc Would you have time to run a few recipes using the new functionality for testing, so we can still include this in v2.1?

[sloosvel]

Works fine in both the area and time preprocessors.