using paste with read.csv inside a function

Question

I want to create a function that uses read.csv() with paste(). The following code works in general

df <- read.csv(paste("/file name", 2010, ".CSV", sep = ""), header = TRUE)

but when I place it inside a function like so

myfunction <- function(date){df <- read.csv(
                             paste("/file name", date, ".CSV", sep = ""),
                             header = TRUE)
                            }

The command myfunction(2010) fails to produce output and does not result in any errors or warnings. What am I doing wrong?

Answer 1

You need to use <<- instead of <-

myfunction <- function(date){df <<- read.csv(
                             paste("/file name", date, ".CSV", sep = ""),
                             header = TRUE)
                            }

or you write:

myfunction <- function(date){read.csv(
                             paste("/file name", date, ".CSV", sep = ""),
                             header = TRUE)
                            }
df <- myfunction(2000)

Answer 2

You could always use sprintf

myfunction <- function(date){
  df <- read.csv(sprintf('/filename%s.csv',date))
  return(df)
}
csv <- myfunction(date)

and if you have lots of dates

ListDates <- as.list(dates)
ListOfCsvs <- lapply(ListDates,myfunction)

EDIT: I didnt make it clear that your issue was solved by return(df) inside myfunction()