Assign a name to a cell while there is a value in another cell in R

Question

There is a df with two columns as follows:

method	Value
H2O	10.2
NA	5.4
NA	NA

I want to assign the word "H2O" to the method column instead of NA if there is a corresponding value (here is 5.4, but any value) in the Value column. So I want the df to look like this:

method	Value
H2O	10.2
H2O	5.4
NA	NA

I am looking for a piece of code in R to do this for my entire table.

Answer 1

1. Indexed assignment:

   df$method[is.na(df$method) & !is.na(df$Value)] <- "H2O"
   df
   #   method Value
   # 1    H2O  10.2
   # 2    H2O   5.4
   # 3   <NA>    NA
   

2. ifelse:

   ifelse(is.na(df$method) & !is.na(df$Value), "H2O", df$method)
   

3. replace (can be safer than ifelse)

   replace(df$method, is.na(df$method) & !is.na(df$Value), "H2O")
   

(2 and 3 need to be assigned back to the column, of course.)