The subsetting implied by the dropList is first applied
to the rollcall object, via dropRollCall.
Then, for each remaining roll call vote, the number of legislators
voting “Yea”, “Nay”, and not voting are computed, using
the encoding information in the codes component of the
rollcall object via the convertCodes
function. The matrix of vote counts are added to the rollcall
object as a component voteMargins.
See Also
dropRollCall on specifying a dropList.
The vote-specific marginals produced by this function are used by as
dropRollCall, summary.ideal and
predict.ideal.