object from which to extract element(s) or in
which to replace element(s).
i
the name of the element we want to extract or
replace.
j
if the element designing by i is complex, j
specifying elements to extract or replace.
drop
For matrices and arrays. If TRUE the result
is coerced to the lowest possible dimension (see the
examples). This only works for extracting elements, not
for the replacement. See drop for further details.