DataArray aware `pint.context`

[LecrisUT]

For example, consider the spectroscopy context:

@context(n=1) spectroscopy = sp

There the conversion depends on the variable n used. Now, consider a DataArray/DataSet where n is a dimension/coordinate. Then when calling DataArray.pint.to("nm") we would want the variable n to be dynamically imported from the current context of the DataArray coordinate.

API-wise I am not sure how that would work, maybe by passing a list/dict of context objects (+ variables)? This might also involve upstream pint support for more complicated context and decorators.

[jmineau]

Is there any support for pint.context right now? I've been trying to get the chemistry context working with the pint.to method, but have not had success.

[jmineau]

Is there any support for pint.context right now? I've been trying to get the chemistry context working with the pint.to method, but have not had success.

Sorry, hgrecco/pint#1559 was actually my issue - trying to convert a flux from particles per area per time to mass per area per time.

[keewis]

no progress (but it looks like you figured that out already). Mostly because I personally have no need for contexts, but in general someone just needs to figure out what would need to be done (and we'd need to figure out a clean way to integrate that in the API). The context manager should already work, though?

[jmineau]

Yeah, the context manager works with simple transformations defined by the context. So for the chemistry context, I can do

da: xr.dataArray
da = da.pint.quantify('particle')
with pint.context('chemistry', mw=16.04 * ureg('g/mol')):
    da_mass = da.pint.to('kg')

but I am working with emissions inventories (ex: EPA Methane Emissions Inventory) which are often given as netcdfs (perfect for xarray) in units of either [substance] / [area] / [time] OR [mass] / [area] / [time]. I want to get all my emission inventories in the same units, but from pint's issue 1559 (linked above), it appears I need to define a custom context to get this to work.

[LecrisUT]

I remember what exactly I was aiming with this issue. Indeed static context can work, but the difficult part is if we want to use an index name or a DataArray as the context variable to convert. For example, let's say we have a dim that has all simulation runs and we associate different values of a refractive index n. Then we might want to plot against wavelength or frequency, in which case we have to do it one slice at a time. It would be better if the pint conversion can extract the dependent dimension and perform xarray operations to do the necessary conversions.

With #163 finished, this might be possible