feature_means
and feature_sds
are provided to allow
alignment of new datasets. For example, after a model is trained, new data
for prediction must be transformed in the same way as the training data to
ensure predictions are valid. If either is NULL
, both will be
computed from Xs
and the output will be internally standardized
(i.e., columns of do.call(rbind, standardizeFeatures(Xs))
will be
have a mean of 0 and a standard deviation of 1).