library(bigtabulate)

# How many samples do we have per year?
bigtable(mort, "year")

 2008  2009  2010  2011  2012  2013  2014  2015 
 8468 11101  8836  7996 10935 10216  5714  6734

# Create nested tables
bigtable(mort, c("msa", "year"))

  2008 2009 2010 2011 2012 2013 2014 2015
0 1064 1343  998  851 1066 1005  504  564
1 7404 9758 7838 7145 9869 9211 5210 6170