CODEWITHSUNDEEP
rlistfunctiondataframe
user9842212
user9842212

Reputation:

Return a list of data.frames created within a function in R

I am trying to reduce duplicated code in a script and in order to do this I am creating some helper functions.

One function I am working on has no arguments that it takes in but rather uses a data set already loaded into the global environment to create a few subsets and then returns those data.frames.

I have created a simple example below that doesn't do exactly what I am describing but will give an idea of how it is structured.

# Create function
my_func <- function(){
  a <- as.data.frame("ID" = c(1, 2, 3, 4, 5, 6), 
                     "TYPE" = c(1, 1, 2, 2, 3, 3), 
                     "CLASS" = c(1, 2, 3, 4, 5, 6))
  b <- as.data.frame("ID" = c(1, 2, 3, 4, 5, 6), 
                     "STATUS" = c(1, 1, 2, 2, 3, 3))
  return(list(a, b))
}

# Call to the function
list[a, b] <- my_func()

The issue I am having is not within the function, but rather when calling the function and trying to store the results. If I call the function like this:

my_func()

It prints the 2 data.frames as a list, however, when trying to assign them names it gives me the error that a does not exist. I am assuming I am just returning them incorrectly or trying to store them incorrectly.

Thanks!

UPDATE

For reference the reason I was trying to use this syntax is due to this post: How to assign from a function which returns more than one value?

Also, I was hoping to capture the return in 1 line instead of having to assign it individually.

For example, in this case it is easy enough to assign it as:

test <- my_func()
a <- test[[1]]; b <- test[[2]]

However, if I had a much longer list, this would get very tedious.

Upvotes: 1

Views: 4631

Answers (2)

Jimmy TwoCents
Jimmy TwoCents

Reputation: 165

Here is a solution for longer lists of data frames.

    my_func <- function(n){
    df_list<-list()
    for (i in 1:n){
    df_list[[i]]<-data.frame('ID'=rep(i,n), 'sqrt'=rep(sqrt(i),n),    'Class'=rep(sample.int(i,1), n))
    
    return(list(my_df=sapply(1:n, function(i)list(df_list[[i]]))))
    }
   output= my_func(10)$my_df[[1]]
   print(output)

If you want to put the dataframes "back together", you can loop through the list with the rbind function to return one frame. This is hopefully what you need. Let me know.

Upvotes: 0

buchmayne
buchmayne

Reputation: 154

The function as.data.frame() converts an existing object to a dataframe. The function data.frame() is what you need to create a data frame. You also don't want to pass in your column names as strings. If you remove the quotes, and change the function to data.frame() it will work!

# Create function
my_func <- function(){
  a <- data.frame(ID = c(1, 2, 3, 4, 5, 6), 
                  TYPE = c(1, 1, 2, 2, 3, 3), 
                  CLASS = c(1, 2, 3, 4, 5, 6))
  b <- data.frame(ID = c(1, 2, 3, 4, 5, 6), 
                  STATUS = c(1, 1, 2, 2, 3, 3))
  return(list(a, b))
}

# Call to the function
test <- my_func()

R functions can only return a single value, so we join a and b into a list and return that. To access the data frames, you can select them by index:

test[[1]]  # returns data.frame 'a' (yes, indices in R start with 1)
test[[2]]  # returns data.frame 'b'

Upvotes: 3

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