如何基于向量创建列

Question

I need to create one column based on two vectors that I had created. This new column need to follow some rules.

Let say I have two vectors:

    vct_A <- c("AAA", "BBB", "CCC", "DDD", "EEE", "FFF")
    vct_B <- c("P1", "P2", "P3")

The rules are:

1. AAA and BBB should consist of P1,P2 and P3
2. CCC consist of P1 and P2
3. DDD consist of P2 and P3
4. EEE and FFF consist of P3

The expected output is a data.frame

     vct_A   vct_B
     <chr>   <chr>   
    1 AAA     P1   
    2 AAA     P2   
    3 AAA     P3   
    4 BBB     P1   
    5 BBB     P2   
    6 BBB     P3   
    7 CCC     P1   
    8 CCC     P2   
    9 DDD     P2   
   10 DDD     P3   
   11 EEE     P4 
   12 FFF     P4 

Really need help on this. Thanks

Answer 1

If there is no logic involved in selecting the values then we have to construct the dataframe manually. One way using expand.grid

df <- rbind(expand.grid(c("AAA", "BBB"), c("P1", "P2", "P3")),
            expand.grid("CCC", c("P1", "P2")),
            expand.grid("DDD", c("P2", "P3")),
            expand.grid(c("EEE", "FFF"), "P3"))
df

#   Var1 Var2
#1   AAA   P1
#2   BBB   P1
#3   AAA   P2
#4   BBB   P2
#5   AAA   P3
#6   BBB   P3
#7   CCC   P1
#8   CCC   P2
#9   DDD   P2
#10  DDD   P3
#11  EEE   P3
#12  FFF   P3

Answer 2

We can use tidyverse methods

library(tidyverse)
list(crossing(Var1 = c("AAA", "BBB"), Var2 = c("P1", "P2", "P3")), 
     crossing(Var1 = "CCC", Var2 = c("P1", "P2")), 
     crossing(Var1 = "DDD", Var2 = c("P2", "P3")), 
     crossing(Var1 = c("EEE", "FFF"), Var2 = "P3")) %>% 
  bind_rows
# A tibble: 12 x 2
#   Var1  Var2 
#   <chr> <chr>
# 1 AAA   P1   
# 2 AAA   P2   
# 3 AAA   P3   
# 4 BBB   P1   
# 5 BBB   P2   
# 6 BBB   P3   
# 7 CCC   P1   
# 8 CCC   P2   
# 9 DDD   P2   
#10 DDD   P3   
#11 EEE   P3   
#12 FFF   P3   

---

or using Map from base R

do.call(rbind, Map(expand.grid, split(vct_A, rep(1:4, c(2, 1, 1, 2))), 
          list(vct_B, vct_B[-3], vct_B[-1], vct_B[3])))