df = data.frame(c("2012","2012","2012","2013"),
                c("AAA","BBB","AAA","AAA"),
                c("X","Not-serviced","X","Y"))
colnames(df) = c("year","type","service_type")

year    type    num_serviced   num_notserviced   num_total
2012    AAA     2              0                 2
...

temp = aggregate(df,
                 list(type = dat_human_errors$type,
                      year = dat_human_errors$year),
                 FUN = function(x){NROW(x)})