I have a list of dataframes which I eventually want to merge while maintaining a record of their original dataframe name or list index. This will allow me to subset etc across all the rows. To accomplish this I would like to add a new variable 'id' to every dataframe, which contains the name/index of the dataframe it belongs to.
Edit: "In my real code the dataframe variables are created from reading multiple files using the following code, so I don't have actual names only those in the 'files.to.read' list which I'm unsure if they will align with the dataframe order:
mylist <- llply(files.to.read, read.csv)
A few methods have been highlighted in several posts: Working-with-dataframes-in-a-list-drop-variables-add-new-ones and Using-lapply-with-changing-arguments
I have tried two similar methods, the first using the index list:
df1 <- data.frame(x=c(1:5),y=c(11:15))
df2 <- data.frame(x=c(1:5),y=c(11:15))
mylist <- list(df1,df2)
# Adds a new coloumn 'id' with a value of 5 to every row in every dataframe.
# I WANT to change the value based on the list index.
mylist1 <- lapply(mylist,
function(x){
x$id <- 5
return (x)
}
)
#Example of what I WANT, instead of '5'.
#> mylist1
#[[1]]
#x y id
#1 1 11 1
#2 2 12 1
#3 3 13 1
#4 4 14 1
#5 5 15 1
#
#[[2]]
#x y id
#1 1 11 2
#2 2 12 2
#3 3 13 2
#4 4 14 2
#5 5 15 2
The second attempts to pass the names() of the list.
# I WANT it to add a new coloumn 'id' with the name of the respective dataframe
# to every row in every dataframe.
mylist2 <- lapply(names(mylist),
function(x){
portfolio.results[[x]]$id <- "dataframe name here"
return (portfolio.results[[x]])
}
)
#Example of what I WANT, instead of 'dataframe name here'.
# mylist2
#[[1]]
#x y id
#1 1 11 df1
#2 2 12 df1
#3 3 13 df1
#4 4 14 df1
#5 5 15 df1
#
#[[2]]
#x y id
#1 1 11 df2
#2 2 12 df2
#3 3 13 df2
#4 4 14 df2
#5 5 15 df2
But the names() function doesn't work on a list of dataframes; it returns NULL. Could I use seq_along(mylist) in the first example.
Any ideas or better way to handle the whole "merge with source id"
Edit - Added Solution below: I've implemented a solution using Hadleys suggestion and Tommy’s nudge which looks something like this.
files.to.read <- list.files(datafolder, pattern="\\_D.csv$", full.names=FALSE)
mylist <- llply(files.to.read, read.csv)
all <- do.call("rbind", mylist)
all$id <- rep(files.to.read, sapply(mylist, nrow))
I used the files.to.read vector as the id for each dataframe
I also changed from using merge_recurse() as it was very slow for some reason.
all <- merge_recurse(mylist)
Thanks everyone.