Output different csv within a function every time we change an argument in R

Question

I have a toy function (for illustration use), within the function i have to produce a csv file with the results Here is my function :

# data #

df <- data.frame(ID = c(1, 2), Obs = c(1.0, 2.0), var=c(2.0,5.0))
 df
  ID Obs var
1  1   1   2
2  2   2   5

# version 1 function
disp <- function(df, c=NULL) {

  if(!is.null(c)){
    tab_res=data.frame(v1=df$ID*2,v2=df$Obs*3,v3=df$var*c)
  }else{
    tab_res=data.frame(v1=df$ID*2,v2=df$Obs*3,v3=df$var)
  }
  
  result=write.csv(tab_res,"test1.csv")
  return(tab_res)
  return(result)
}

# current output 
disp(df,c=NULL)
  v1 v2 v3
1  2  3  2
2  4  6  5
 disp(df,c=1)
  v1 v2 v3
1  2  3  2
2  4  6  5
 disp(df,c=2)
  v1 v2 v3
1  2  3  4
2  4  6 10

# it produced also a csv file with exacte tables

What i need is whenever i change an argument in my function, it will produce a different csv file with the appropriate name (chosen by the user). This is what i did, it is working, but i was wondering if there is any other efficient way, in addition i do not see the column names in the csv files (when i try to set col.names to TRUE, it gives me an error).

# modified function version 2
disp <- function(df, c=NULL, output_name) {

  if(!is.null(c)){
    tab_res=data.frame(v1=df$ID*2,v2=df$Obs*3,v3=df$var*c)
  }else{
    tab_res=data.frame(v1=df$ID*2,v2=df$Obs*3,v3=df$var)
  }
  
  result=write.csv(tab_res,"test1.csv")
  csv_name <- paste0("test1_", output_name, ".csv") 
  result=write.table( tab_res,  
                      file=csv_name, 
                      append = T, 
                      sep=',', 
                      row.names=F, 
                      col.names=F,
                      quote=T)
  return(tab_res)
  return(result)
  
}

disp(df,c=NULL,"no_c")
  v1 v2 v3
1  2  3  2
2  4  6  5

# it produces a csv file test1_no_c

Thank you in advance for your help!

Answer 1

Here is a solution that works whether the file already exists or not. It uses the return value of file.exists to set append and col.names values.

disp <- function(df, output_name, c = NULL) {
  df$ID <- df$ID*2
  df$Obs <- df$Obs*3
  if(!is.null(c)){
    df$var <- df$var*c
  }
  names(df) <- paste0("v", 1:3)
  
  csv_name <- paste0("test1_", output_name, ".csv")
  fexists <- file.exists(csv_name)
  write.table(df, file = csv_name, 
              sep = ",",
              append = fexists,
              row.names = FALSE, 
              col.names = !fexists,
              quote = TRUE)
  df
}

disp(df, "no_c")
disp(df, "no_c", c = 1)
disp(df, "no_c", c = 2)