[R] Create New Column Inside Data Frame for Many Data Frames

[Jeff Newmiller]

I suggest you read the section on indexing in the Introduction to R document that comes with R. In particular, look at the [[i]] notation. This comes in handy in a couple of ways.

First, you shouldn't be working with "many" data frames at once that are stored as separately-named objects. If you plan to do similar things to them, then you should store them in a list:

myframes <- list()
myframes[["A"]] <- data.frame(population=c(100, 300, 5000, 2000, 900, 2500))

Secondly, you can programmatically access the columns in a data frame if needed:

i <- "A"
dest <- "Rate"

myframes[[i]][[dest]]<-ROC(myframes[[i]][["population"]])

Study up on indexing in R... much of the power of this language lies there.

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Sent from my phone. Please excuse my brevity.

"Sparks, John James" <jspark4 at uic.edu> wrote:

>Dear R Helpers,
>
>I have a large number of data frames and I need to create a new column
>inside each data frame.  Because there is a large number, I need to
>"loop"
>through this, but I don't know the syntax of assigning a new column
>name
>dynamically.
>
>Below is a simple example of what I need to do.  Assume that I have to
>do
>this for all 26 letters and you should see the form of the problem.
>
>Any help would be much appreciated.  If more information is needed,
>please
>let me know.
>
>Many thanks.
>--John Sparks
>
>
>
>library(quantmod)
>A <- data.frame(population=c(100, 300, 5000, 2000, 900, 2500))
>A$Rate<-ROC(A["population"])
>
>B <- data.frame(population=c(200, 300, 4000, 3000, 2000, 500))
>B$Rate<-ROC(B["population"])
>
>letters<-c("A","B")
>length(letters)
>
>#for (i in letters){
># HELP!
>#}
>
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