Add additional data to the accumulator value.
Add additional data to the accumulator value. Is allowed to modify and return r
for efficiency (to avoid allocating objects).
the new value of the accumulator
Merge two accumulated values together.
Merge two accumulated values together. Is allowed to modify and return the first value for efficiency (to avoid allocating objects).
both data sets merged together
Return the "zero" (identity) value for an accumulator type, given its initial value.
Return the "zero" (identity) value for an accumulator type, given its initial value. For example, if R was a vector of N dimensions, this would return a vector of N zeroes.
(Since version 1.3.0)