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?

GKi · Accepted Answer · 2019-05-21T07:08:30.757

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)

JMilner · Answer 2 · 2019-05-21T22:29:10.163

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()

edited May 21 '19 at 22:29

answered May 21 '19 at 07:08

JMilner

491
4
12

score 0 · Answer 3 · answered May 21 '19 at 07:05

Return the dataframe from your function

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

and assign it

df <- myfunction(2010)

In R, the last line in the function is automatically returned anyway, so this should also work.

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

using paste with read.csv inside a function

3 Answers3