dplyr::group_by - Change name of second group-CodePudding

I'd like to group by two columns, and for the third column I'd like the value to remain same for the first group but changed to 'D5_repeat' for second group.

df <- data.frame(x = c(rep('A',2), rep('B',2)),
                 y = c(rep('Zebra',4), rep('Lion',4)),
                 z = c(rep('D5',4), rep('D10',4)))

df %>%
  group_by(x,y) %>%
  ...

Results

#A tibble: 8 × 3
  x     y     z         
  <chr> <chr> <chr>     
1 A     Zebra D5        
2 A     Zebra D5 
3 B     Zebra D5_repeat        
4 B     Zebra D5_repeat 
5 A     Lion  D10       
6 A     Lion  D10
7 B     Lion  D10_repeat       
8 B     Lion  D10_repeat

CodePudding user response：

I think this is what're looking for?

df %>%
  group_by(x,y) %>%
  mutate(z = paste0(z, if_else(row_number() > 1, "_repeat", ""))) %>%
  ungroup()

Result

# A tibble: 8 × 3
  x     y     z         
  <chr> <chr> <chr>     
1 A     Zebra D5        
2 A     Zebra D5_repeat 
3 B     Zebra D5        
4 B     Zebra D5_repeat 
5 A     Lion  D10       
6 A     Lion  D10_repeat
7 B     Lion  D10       
8 B     Lion  D10_repeat

CodePudding user response：

You could use match(x, unique(x)) to get the group numbers of x in each y group.

library(dplyr)

df %>%
  group_by(y) %>%
  mutate(z = ifelse(match(x, unique(x)) > 1, paste0(z, '_repeat'), z)) %>%
  ungroup()

# # A tibble: 8 × 3
#   x     y     z
#   <chr> <chr> <chr>     
# 1 A     Zebra D5
# 2 A     Zebra D5
# 3 B     Zebra D5_repeat
# 4 B     Zebra D5_repeat
# 5 A     Lion  D10
# 6 A     Lion  D10
# 7 B     Lion  D10_repeat
# 8 B     Lion  D10_repeat