Catch the exception for the R2 computation

[xiki-tempula]

In
https://github.com/OpenFreeEnergy/arsenic/blob/main/arsenic/stats.py#L81-L83
The scipy.stats.linregress were used to find the R2.
In the older versions (scipy<1.8) when both x and y are the same value, for example:

import scipy
slope, intercept, r_value, p_value, std_err = scipy.stats.linregress([1.33, 1.33, 1.33], [0.33, 0.33, 0.33])

will return a runtime warning.
Now this would return a ValueError, it might be good to catch this exception and return 0? Thanks.

The code to reproduce this error is

from openff.arsenic.stats import bootstrap_statistic
bootstrap_statistic([1.33, 2.00], [0.33, 1.00], statistic="R2")

[mikemhenry]

@xiki-tempula thanks for this bug report!

I'm a little unsure why returning 0 is appropriate if y_true_sample != y_pred_sample Or are you saying that when y_true_sample is the same as y_pred_sample, scipy throws a ValueError?

[xiki-tempula]

@mikemhenry Thanks for the reply. Sorry I have missed this message. I wonder if it is possible to allow arsenic to handle

from openff.arsenic.stats import bootstrap_statistic
bootstrap_statistic([1.33, 2.00], [0.33, 1.00], statistic="R2")

Currently, this would give ValueError.