Helper function to obtain the observed exposure for the Aronow and Samii estimator
Source:R/helpers-experiments-over-networks.R
get_exposure_AS.RdSee https://book.declaredesign.org/experimental-causal.html#experiments-over-networks
R/helpers-experiments-over-networks.R
get_exposure_AS.RdSee https://book.declaredesign.org/experimental-causal.html#experiments-over-networks