R：重复 data.frame 的行 k 次并为新行值添加前缀

Question

I know from this answer how to duplicate rows of a dataframe. That's fine if you want to repeat the rows n times.

I want to do something similar but to also add a prefix within a column of newly added rows. Note: I am not basing the repetition count on the number of rows. It needs to be provided by a parameter (call it k).

So the operation should look like this assuming I want to repeat the dataframe k=3 times:

Input:

data.frame(a = c("1","2","3", "4"),b = c(1,2,3, 4))
  a b
1 "1" 1
2 "2" 2
3 "3" 3
4 "4" 4

Output:

  a b
1 "1" 1
2 "2" 2
3 "3" 3
4 "4" 4
5 "1_1" 1
6 "1_2" 2
7 "1_3" 3
8 "1_4" 4
9 "2_1" 1
10 "2_2" 2
11 "2_3" 3
12 "2_4" 4

What's a nice R way to do this??

Answer 1

You could use expand_grid (assuming your data.frame is named df1 ):

library(dplyr)
library(tidyr)

expand_grid(a = df1$a, b = df1$b) %>% 
  mutate(a = paste(a, b, sep = "_")) %>% 
  bind_rows(df1, .)

This returns

     a b
1    1 1
2    2 2
3    3 3
4  1_1 1
5  1_2 2
6  1_3 3
7  2_1 1
8  2_2 2
9  2_3 3
10 3_1 1
11 3_2 2
12 3_3 3

Answer 2

Using tidyverse with crossing

library(tidyr)
library(dplyr)
 data.frame(a = c("1","2","3"),b = c(1,2,3)) %>%
   add_row(crossing(!!! .) %>%
   unite(a, a, b, remove = FALSE))

-output

     a b
1    1 1
2    2 2
3    3 3
4  1_1 1
5  1_2 2
6  1_3 3
7  2_1 1
8  2_2 2
9  2_3 3
10 3_1 1
11 3_2 2
12 3_3 3