## First put all file names into a list
library(data.table)
files <- list.files(path = "F:\MUMuniv\machine learning class\
                        price sensitivty\PS works\Customer files",
                        pattern = ".xls", full.names = T)


readdata <- function(fn){
  dt_temp <- fread(fn)
  return(dt_temp)
}

# then using

all.files <- lapply(files, readdata)
final.data <- rbindlist(all.files)