na.delete.RdDoes row-wise deletion as na.omit, but adds frequency of missing values
for each predictor
to the "na.action" attribute of the returned model frame.
Optionally stores further details if options(na.detail.response=TRUE).
na.delete(frame)a model frame with rows deleted and the "na.action" attribute added.
# options(na.action="na.delete")
# ols(y ~ x)