R 数据表：为每一行从其他表生成随机值

我想通过从模拟表(table\simul)生成航班号来模拟航班号，以观察表为基础.

table_simul <- data.table(
  date_f = c("2020-01-01","2020-01-02","2020-01-03","2020-01-03"),
  city = c("Paris","Paris","London", "Berlin")
)

table_obs <- data.table(
  city = c("Paris","Paris","Paris","London","London", "Berlin"),
  flight = c(1,2,7,4,5,14),
  weight = c(0.33,0.33,0.33,0.5,0.5,1)
)

使用的数据:

 Table simul:
    
date        city

2020-01-01  Paris
2020-01-01  Paris
2020-01-01  London
2020-01-01  Berlin


Table obs
---------
city   flight   weight

Paris   1        0.33
Paris   2        0.33
Paris   7        0.33
London  4        0.5
London  5        0.5
Berlin  14       1

预期结果:

date_f        city     flight
2020-01-01  Paris       2
2020-01-02  Paris       2
2020-01-03  London      4
2020-01-03  Berlin      14

我想使用数据表包，因为数据量非常大.

get_flight_sample <- function(param_city){
  table_simul[city==param_city]
  res <- sample(table_obs$flight,1, replace=T, prob = table_obs$weight)
}

res <- table_simul[,.(flight = get_flight_sample(city))]