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

March 21, 2022

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"
))

>Solution :

I think this approach is extensible to many more conditions assuming yours is the minimal example and you have a larger more complicated dataset.

library(dplyr)

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"
))

df2 <- data.frame(Type2 = c("N", "N"), Grade = c("S", "W"))

df %>%
    select(Type, Result) %>%
    left_join(df2, by = c("Type" = "Type2")) %>%
    mutate(Grade = case_when(Type == "S" ~ "S", Type == "W" ~ "W", TRUE ~ 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