# d.s
# d = first and last names of four children, and ages
# no keys need be present
# bill jones' age is unknown
# there are no records for the kennedy family
d1_c("mary","bill","dave","jerry","sally")
d2_c("jones","jones","thompson","smith","thompson")
d3_c(12,NA,7,10,11)
d_cbind(d1,d2,d3)