What is causing "No non-missing arguments to max; returning -Inf"?

I have a function which will draw specific lines on my plot, defined as

MaxLines <- function(df,df_col_1,df_col_2){
  data.frame(df_col_1 = c(rep(df$df_col_1[which.max(df$df_col_2)], 2),
                                           -Inf), 
                       df_col_2 = c(-Inf, rep(max(df$df_col_2), 2)))
  
}

When I try to call this function I get the error mentioned in the title.

col_1 = c(5,6,7)
col_2 = c(1,2,3)
foo <- data.frame(col_1,col_2)
MaxLines(foo,col_1,col_2)


------------------------------------------------
new_1 new_2
1  -Inf  -Inf
2  -Inf  -Inf
3  -Inf  -Inf
Warning message:
In max(df$df_col_2) : no non-missing arguments to max; returning -Inf

I expect the function to return

But it does not. When inputting into the function directly ie.

MaxLines <- data.frame(col_1 = c(rep(foo$col_1[which.max(foo$col_2)], 2),
                                           -Inf), 
                       col_2 = c(-Inf, rep(max(foo$col_2), 2)))

I get the correct output, so it seems to just be the calling of the function.

>Solution :

Base R functions don’t easily allow you to pass in unquoted column names. You can either convert the symbols to strings

MaxLines <- function(df,df_col_1,df_col_2){
  df_col_1<-as.character(substitute(df_col_1))
  df_col_2<-as.character(substitute(df_col_2))
  data.frame(df_col_1 = c(rep(df[[df_col_1]][which.max(df[[df_col_2]])], 2),
                          -Inf), 
             df_col_2 = c(-Inf, rep(max(df[[df_col_2]]), 2)))
  
}
MaxLines(foo,col_1,col_2)

or you can pass in strings

MaxLines <- function(df,df_col_1,df_col_2){
  data.frame(df_col_1 = c(rep(df[[df_col_1]][which.max(df[[df_col_2]])], 2),
                          -Inf), 
             df_col_2 = c(-Inf, rep(max(df[[df_col_2]]), 2)))
  
}
MaxLines(foo,"col_1","col_2")