R- how to dynamically name data frames?

Question

I have two types of files in my directory. Each type has either the text "Drug_Rep" in it or if its not there it means its a control file. Drug data has replicates which can vary in number and so does the control. I am reading the files in a for loop as follows. I want to name my dataframes as X_Drug_Rep1 and then the next as X_Drug_Rep2 and so on...and save the dataframe for further processing. Do the same for controls...X_CONTROL_Rep1...X_CONTROL_Rep2...and so on. What is the syntax to save my data into dataframes because i need to do some merges and calculations later on the drug replicate dataframes and controls separately. paste on the left side of assignment does not seem to work. Any suggestions?

for (f in 1:length(fileList)){
    fileName <- fileList[f]
    X <-read.xls(fileName)

    if(regexpr("Drug_Rep", fileName)[1]>0){
      print("DRUG")
      print(fileName)
      paste(X_Drug_Rep,i)<-X
      i=i+1
    }
    else{
      print("CONTROL")
      print(fileName)
      paste(X_CONTROL,j)<-X
      j=j+1
    }
  }

Solution

OP is really struggling so instead of a long comment, I'll show him here. Don't care if this gets closed.

The technical (don't do that answer) would be to use assign:

i <- 1
j <- 1
for (f in 1:length(fileList)){
    fileName <- fileList[f]
    X <-read.xls(fileName)

    if(grepl("Drug_Rep", fileName)) {
      print("DRUG")
      print(fileName)
      assign(paste("X_Drug_Rep", i, sep = '_'), X)
      i <- i+1
    } else {
      print("CONTROL")
      print(fileName)
      assign(paste("X_CONTROL", i, sep = '_'), X)
      j <- j+1
    }
  }

But as we recommended, you should use lists instead. Using a for loop, it would look like this:

X_Drug_Rep <- list()
X_CONTROL  <- list()
i <- 1
j <- 1
for (f in 1:length(fileList)){
    fileName <- fileList[f]
    X <-read.xls(fileName)

    if(grepl("Drug_Rep", fileName)) {
      print("DRUG")
      print(fileName)
      X_Drug_Rep[[i]] <- X
      i <- i+1
    } else {
      print("CONTROL")
      print(fileName)
      X_CONTROL[[j]] <- X
      j <- j+1
    }
  }

Finally, how your code would look like without a for loop:

drug.rep.files <- grep("Drug_Rep", fileList, value = TRUE)
control.files  <- grep("Drug_Rep", fileList, value = TRUE, invert = TRUE)

X_Drug_Rep <- lapply(drug.rep.files, read.xls)
X_CONTROL  <- lapply(control.files, read.xls)

Much shorter, no?! Again, this creates two lists. For example, instead of X_Drug_Rep_1, you would access the first Drug_Rep item by doing X_Drug_Rep[[1]].