setwd("C:\\Users\\fxc\\Desktop")
Revenue <- read.table("2014.txt", header = TRUE)
Revenue$Stkcd <- factor(Revenue$Stkcd)
AllFirms <- unique(Revenue$Stkcd)
Firm.1 <-Revenue[Revenue$Stkcd == "1",]
Rev <- Firm.1[1:60,]
for (i in AllFirms){
  Firm.i <-Revenue[Revenue$Stkcd == "i",]
  Revenue.i <- Firm.i[1:60,]
  Rev <- cbind(Rev, Revenue.i)
}
为什么最后REV里面都是NA？