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Units for .var, .std methods on offset units. #1640

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andrewgsavage opened this issue Oct 28, 2022 · 0 comments · May be fixed by #1992

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andrewgsavage commented Oct 28, 2022

pint-pandas sets units for reductions on offset units incorrectly.

Statistical reductions like .std and .var compute quantities related to the spread of a distribution. As such, the result should always be a delta-unit (i.e. non-offset unit), regardless if the input has an offset or not. Currently, the result is wrongly reported with offset units if the input has offset units.
hgrecco/pint-pandas#94

I wanted to use the pint implementation, but that is also incorrect:

import pint
import numpy as np

q = pint.Quantity([1,2,4], "degC")

q.std() # OffsetUnitCalculusError
np.std(q) # OffsetUnitCalculusError
np.var(q) # OffsetUnitCalculusError

q.var() 
1.5555555555555554 degree_Celsius2

andrewgsavage linked a pull request

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delta units for std, var #1992

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