Mutate a column and fill its value from another column based on matchin gof two columns

Question

I have a df

Type             Total      
Apple              6
Banana             2
Grapes             7
Unidentified       8

I want to replace the Unidentified Type value with another type (Dominant Type) that has the highest Total value. From the above example, Grapes because the Total value of Grapes 7 is the highest from all the other Total values excluding Unidentified.

Type             Total          Dominant Type
Apple              6                 NA
Banana             2                 NA
Grapes             7                 NA
Unidentified       8               Grapes

How would I complete this in dplyr?

Answer 1

Use mutate to create a new column which is conditional upon Type being equal to Unidentified; if it is, then set it equal to the maximum value of Total, excluding the value of Total which corresponds to Unidentified.

df = fread('Type             Total      
Apple              6
Banana             2
Grapes             7
Unidentified       8')

df %>% 
    dplyr::mutate(
        `Dominant Type` = ifelse(Type == "Unidentified", 
            Type[which.max(Total[!Type=="Unidentified"])], 
            NA
            )
        )

           Type Total      Dominant Type
1:        Apple     6   <NA>
2:       Banana     2   <NA>
3:       Grapes     7   <NA>
4: Unidentified     8 Grapes