Function to create new variable by multiple conditions using mutate and case_when (R)

Question

I'm trying to create a function that will compare variables 1 and 2 and create a third variable based on whether they match. I need to do this >25 times (for different combinations of variables), which is why I want to create a function instead of just using mutate and case_when.

I'm pretty new to R, so this is mostly cobbled together from other helpful stack overflow posts and miscellaneous tutorials.

Here's what I tried:

determine_match <- function(df, col_a, col_b){


col_a <- enquo(col_a)
  col_b <- enquo(col_b)
  newvar <- paste0(quo_name(col_a), quo_name(col_b))
  df <- df %>% mutate(!!newvar:= case_when(
    !!col_a == '1' & !!col_b =='Yes' ~ 'Match',
    !!col_a == '0' & !! col_b == 'No' ~ 'Match',
    !!col_a == '1' & !!col_b == 'No' ~ 'No Match',
    !!col_a == '0' & !!col_b == 'Yes' ~ 'No Match',
    is.na(!!col_a) | is.na(!!col_b) ~ NA_character_,
    TRUE ~ 'Error'
  )) 
}

And I tested it on this data set:

test1 <- c('1', '0', '1', '1', '0', NA)
test2 <- c('Yes', 'No', 'No,', NA, 'Yes', NA)
id <- c(1,2,3,4,5,6)
testing.df <- data.frame(id, test1, test2)

I'm not getting errors, but when I run the function with a print statement, it only returns the string name for newvar and doesn't change the actual data frame.

I also tried testing.df %>% mutate(testing3 = funs(determine_match(testing.df, testing1, testing2))) and testing3 gives me ~determine_match(testing.df, testing1, testing2)

Not sure if the problem is the function, the attempt to apply, or both.

Hope some kind soul can help, thank you!!

Answer 1

You need to return the result, add return(df) (or even just df ) as the last line of your function.

If you're not worried about input values other than the ones you explicitly mention, ( "0" , "1" , NA for col_a , and "Yes" , "No" , NA for col_b ), you could simplify the condition to this (for some definitions of "simplify"---it's definitely shorter).

determine_match <- function(df, col_a, col_b) {
  col_a <- enquo(col_a)
  col_b <- enquo(col_b)
  newvar <- paste0(quo_name(col_a), quo_name(col_b))
  df <- df %>% mutate(
    !!newvar := 
      c("No Match", "Match")[((!!col_a == '1') == (!!col_b == 'Yes')) + 1]
    )
  return(df)
}