Replace a value based on a condition

Question

I have the following dataframe

df <- data.frame(drug = c("__Drug A__", "__NA__", "__Drug B__", "__NA__", "__Drug C__", "__NA__"))

and would like to replace __NA__ values with a preciding value so that the final column will be

df <- data.frame(drug = c("__Drug A__", "__Drug A__", "__Drug B__", "__Drug B__", "__Drug C__", "__Drug C__"))

Any help will be appreciated. Thanks in advanceQ

Answer 1

You could first replace the values with NA and after that fill them down like this:

library(dplyr)
library(tidyr)
df %>%
  mutate(drug = na_if(drug, "__NA__")) %>%
  fill(drug, .direction = "down")
#>         drug
#> 1 __Drug A__
#> 2 __Drug A__
#> 3 __Drug B__
#> 4 __Drug B__
#> 5 __Drug C__
#> 6 __Drug C__

^{Created on 2024-02-22 with reprex v2.0.2}