R中两个数据帧上的条件JOIN

Question

Suppose there are two data frames likes the following (given from this post ):

df1 = data.frame(CustomerId = c(1:6), Product = c(rep("Toaster", 3), rep("Radio", 3)))
df2 = data.frame(CustomerId = c(2, 4, 6), State = c(rep("Alabama", 2), rep("Ohio", 1)))

df1
#  CustomerId Product
#           1 Toaster
#           2 Toaster
#           3 Toaster
#           4   Radio
#           5   Radio
#           6   Radio

df2
#  CustomerId   State
#           2 Alabama
#           4 Alabama
#           6    Ohio

The question is how can I do the following sql query in R:

SELECT * FROM df1 JOIN df2 on df1.CustomerId <= df2.CustomerId

What I have known is that I can do the inner join using merge(df1, df2, by = "CustomerId") . But it is not satisfied the condition of the join.

Answer 1

This one confusing way to do this. But it works though:

library(tidyverse)
df1 = data.frame(CustomerId = c(1:6), Product = c(rep("Toaster", 3), rep("Radio", 3)))
df2 = data.frame(CustomerId = c(2, 4, 6), State = c(rep("Alabama", 2), rep("Ohio", 1)))

map2_df(
  df1$CustomerId, df1$Product,
  .f = ~ {
    temp <- df2 %>% filter(.x <= CustomerId)
    tibble(CustomerId.x = .x, Product = .y, 
           CustomerId.y = temp$CustomerId, State = temp$State)
  }
)

Answer 2

As I found in comments by dear Grothendieck, one straightforward solution is using sqldf package and get exactly my result in sql format:

library(sqldf)
sqldf("SELECT * FROM df1 JOIN df2 on df1.CustomerId <= df2.CustomerId")