NA
s such that all lists are
the same lengthAdds NA
values to the end of each list in a list of lists such that
they all become the length of the longest list. The longest list will not
have any NA
s added to it.
na_pad(x, y)
a list of lists with each sub-list the same length
a list of lists, with sub-lists having different lengths
a list of the number of NA
values to append to each sub-list