how to duplicate rows with certain condition and create anew variable at the same time

Question

I have a df like below and I would like to transfer it to sth like the table on the right, how can I duplicate the rows with Type=="N" and add new var Grade?

Basically, if Type==N, then Grade can be S or W, that is why we need to duplicate the rows.

df<-structure(list(Type = c("N", "N", "S", "W"), Result = c(8, 9, 
7, 6)), row.names = c(NA, -4L), class = c("tbl_df", "tbl", "data.frame"
))

Answer 1

Using some functions from tidyverse, you can use crossing to duplicate rows and add the "Grade" column at the same time, then filter to match your stated rules.

library(tidyverse)

result <- df %>% 
  crossing(data.frame(Grade = c('S', 'W'))) %>% 
  filter(Type == 'N' | Type == Grade)

  Type  Result Grade
  <chr>  <dbl> <chr>
1 N          8 S    
2 N          8 W    
3 N          9 S    
4 N          9 W    
5 S          7 S    
6 W          6 W