List as input of a function

Question

I (as a beginner in R) am trying to pass a list of dataframes as an input of a function to change some variables from char to dates. When I run the script it works. If I then try it in a function I don't get any error but the type of the variable is still a character. Below you can find the function. Thank you in advance for your suggestions.

data <- list(complaints,credit,customers,delivery,subscriptions,formula)

building <- function(x){
for (i in 1:6){
vars <- which(names(x[[i]]) %in% c("StartDate","EndDate","PaymentDate","RenewalDate","ProcessingDate","ComplaintDate","DOB"))

x[[i]][,vars] <- sapply(vars,function(vars) as.Date(x[[i]][,vars],format=f),simplify=FALSE)
}

complaints <- x[[1]]

credit <- x[[2]]

customers <- x[[3]]

delivery <- x[[4]]

subscriptions <- x[[5]]

formula <- x[[6]]
}

building(data)

you have to return your fixed data, e.g. data2 <- building(data) — Karl Forner, Feb 26 '14 at 09:05
If you provide a reproducible exampled and tell us what your desired output is, we can probably do a lot more. See http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example on how to provide encapsulated data. — Roman Luštrik, Feb 26 '14 at 09:07

score 1 · Accepted Answer · answered Feb 26 '14 at 09:08

You are trying to modify objects in your function that were defined outside of the function. This is called side effect in computer science: http://en.wikipedia.org/wiki/Side_effect_%28computer_science%29

You cannot do that in R.

Instead, you can do, for example that :

data <- list(complaints,credit,customers,delivery,subscriptions,formula)

building <- function(x){
for (i in 1:6){
vars <- which(names(x[[i]]) %in% c("StartDate","EndDate","PaymentDate","RenewalDate","ProcessingDate","ComplaintDate","DOB"))

x[[i]][,vars] <- sapply(vars,function(vars) as.Date(x[[i]][,vars],format=f),simplify=FALSE)
}

return(x)
}

output <- building(data)

complaints <- output [[1]]

credit <- output [[2]]

customers <- output [[3]]

delivery <- output [[4]]

subscriptions <- output [[5]]

formula <- output [[6]]

List as input of a function

1 Answers1