ff) vector y to ff vector
x. Please note that the data of x will be
coerced to the type of y if y has a higher
vmode.ffappend(x, y, adjustvmode = TRUE, ...)ff object where data will be appended to.
If x==NULL a new ff object will be createdff object or vector objectvmode to make sure y is appended without
loss of information.chunk interallyff object with same physical storage as x
unless y has a higher vmode in which case
the data will be cloned to the higher vmodec.ff