Map_rect with a ragged array

I’ve successfully implemented map_rect() for rectangular data structures, but I now have missing data in each column variable such that I’ll need to pass a ragged array to the map_rect() function.

The only way I can think of doing this is to create a matrix with the number of rows as large as the longest vector in the raw data. Then, I suppose I would fill each row with as much data as necessary, and leave the remaining cells unfilled or filled with zeros. Is there a better way to do this?