Loop through dataframe variables in R

Question

I have a few dataframes with only a few variables different from each other. Mostly they are the same. I would like to prepare the variables in a loop, so I do not have to specify each and every variable for all my dataframes separately. I'm however running into some issues.

clist <- c("data", "data_error", "data_RT")

I first made a list of the names of my dataframes

for (i in clist) {
i$ID <- as.factor(i$ID)
i$TMS <- as.factor(i$TMS)
i$bias<- as.numeric(i$bias)
 ... }

The I try to loop over all the variables I want to prepare. This is however not possible and I get an error message saying:

Error in i$ID : $ operator is invalid for atomic vectors

I tried google for help, but I did not understand the explanations for it :( Could you help me understand what I'm doing wrong and how I could solve it?

The $-operator doesn't work dynamically. Use i[,"ID"] <- as.factor(i[,"ID"]) .... — Andre Elrico
– Andre Elrico, Commented Sep 26, 2017 at 11:02
also you need the dataframes in clist as object_names and not as strings. — Andre Elrico
– Andre Elrico, Commented Sep 26, 2017 at 11:04
Hi Andre! Thanks for the hint! It however still produces an error. I changed it now to: clist <- c(data, data_error, data_RT) for (i in clist) { i[,"ID"] <- as.factor(i[,"ID"]) } but it tells me Error in [.default(i, , "ID") : incorrect number of dimensions. This confuses me, because if I just replace the "i" with "data" (as I intend the loop to do) data[,"ID"] <- as.factor(data[,"ID"]), it does work... Any thoughts on where the dimension mismatch might stem from? — Inkling
– Inkling, Commented Sep 26, 2017 at 11:25

LAP · Accepted Answer · 2017-09-26 11:45:00Z

2

You could use a list of dataframes instead of a vector of names:

clist <- list(data, data_error, data_RT)

Then loop through the list:

for (i in 1:length(clist)) {
clist[[i]]$ID <- as.factor(clist[[i]]$ID)
clist[[i]]$TMS <- as.factor(clist[[i]]$TMS)
clist[[i]]$bias<- as.numeric(clist[[i]]$bias)
 ... }

Afterwards, you can use

list2env(clist,globalenv())

to put the dataframes back into your global environment. I would advise you to just keep them inside the list, though.

answered Sep 26, 2017 at 11:45

LAP

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