logical. Should missing values (including NaN) be removed?
Value
HD17
Formula
$$HD17_j = \sum_{j-1}^{I} (17 ^ oC - TG_ij)$$
References
Quayle, R. G., & Diaz, H. F. (1980). Heating degree day data applied to residential heating energy consumption. Journal of Applied Meteorology, 19(3), 241-246. https://doi.org/10.1175/1520-0450(1980)019<0241:HDDDAT>2.0.CO;2