R: How to write a user-defined function that can repeatedly append data frames to a (growing) existing list?

Question

I want a function that I can call several times throughout a data analysis script, each time appending a new data frame to an existing list.

myList <- list()

The function creates a new data frame after subsetting an existing data frame, and then appends this new data frame to my list (in theory).

appendList = function(){
  df = mydf[mydf$myData < 0.5, ]
  myList[[(length(myList)+1)]] <- df
}

In my real-world problem I have several different code chunks, each with a different set of data in the column 'myData'.

I thought I could just use my function above like this:

mydf <- data.frame(myData = runif(10))
appendList()

mydf <- data.frame(myData = rnorm(10))
appendList()

But my list remains unchanged:

length(myList)
>[1] 0

Is it an environment issue?

My goal is for 'myList' to contain all of these different data frames.

Bonus: Perhaps there is a better way to complete this kind of task?

You need to assign the results of `appendList` back to your original `myList` - like: `myList — thelatemail, Nov 20 '15 at 00:04
You'd need to change your line to `myList[[(length(myList)+1)]] < — David Robinson, Nov 20 '15 at 00:08
@thelatemail It does in this case, and I was oversimplifying since this isn't the best solution anyway. (btw, the solution of `myList — David Robinson, Nov 20 '15 at 00:21
@DavidRobinson - true, the last line of `appendList` should be `return(myList)` or `myList`, then `myList — thelatemail, Nov 20 '15 at 00:35
These are all helpful comments. Since I figured out how many data frames I'll need, I elected to make a list of subsets at the end of the script with `lapply` as @thelatemail suggests. — BDA, Nov 20 '15 at 17:39

0 Answers0