Duplicate Values From Previous Row For Same Subject in R

Question

Assume df which looks like this:

subjectid	event	led1	led2
ABCD_1234	base	22.5	50.3
ABCD_1234	followup	NA	NA
ABCD_3456	base	11.2	-23.87
ABCD_3456	followup	NA	NA
ZXRT_5555	base	NA	-0.9
ZXRT_5555	followup	NA	NA
EFGH_8976	base	NA	NA
EFGH_8976	followup	NA	NA

How can one duplicate the values in rows where event is base to the followup rows for led1 and led2?

Output:

subjectid	event	led1	led2
ABCD_1234	base	22.5	50.3
ABCD_1234	followup	22.5	50.3
ABCD_3456	base	11.2	-23.87
ABCD_3456	followup	11.2	-23.87
ZXRT_5555	base	NA	-0.9
ZXRT_5555	followup	NA	-0.9
EFGH_8976	base	NA	NA
EFGH_8976	followup	NA	NA

Answer 1

You can use across to perform operation on all columns that starts with "led". When the event column equals "followup" and at the same time the led column is NA, fill the led column with values at event equals "base".

library(dplyr)

df %>% 
  mutate(across(starts_with("led"), ~ifelse(event == "followup" & is.na(.x), .x[event == "base"], .x)), 
         .by = subjectid)

#>   subjectid    event led1   led2
#> 1 ABCD_1234     base 22.5  50.30
#> 2 ABCD_1234 followup 22.5  50.30
#> 3 ABCD_3456     base 11.2 -23.87
#> 4 ABCD_3456 followup 11.2 -23.87
#> 5 ZXRT_5555     base   NA  -0.90
#> 6 ZXRT_5555 followup   NA  -0.90
#> 7 EFGH_8976     base   NA     NA
#> 8 EFGH_8976 followup   NA     NA