R: Avoid repeating lines of code using R subsets in scripts - r

Question

I'm very new to R - but have been developing SAS-programs (and VBA) for some years. Well, the thing is that I have 4 lines of R-code (scripts?) that I would like to repeat 44 times. Two times for each of 22 different train stations, indicating whether the train is in- or out-going. The four lines of code are:
dataGL_FLIin <- subset( dataGL_all, select = c(Tidsinterval, Dag, M.ned, Ugenr.,Kode, Ugedag, FLIin))
names(dataGL_FLIin)[names(dataGL_FLIin)=='FLIin'] <- 'GL_Antal'
dataGL_FLIin$DIR<-"IN"
dataGL_FLIin$STATION<-"FLI
To avoid repeating the 4 lines 44 times I need 2 "macro variables" (yes, I'm aware, that this is a SAS-thing only, sorry). One "macro variable" indicating the train station and one indicating the direction. In the example above the train station is FLI and the direction is in. Below the same 4 lines are demonstrated for the train station FBE, this time in out-going direction.
dataGL_FBEout <- subset( dataGL_all, select = c(Tidsinterval, Dag, M.ned, Ugenr.,Kode, Ugedag, FBEout))
names(dataGL_FBEout)[names(dataGL_FBEout)=='FBEout'] <- 'GL_Antal'
dataGL_FBEout$DIR<-"OUT"
dataGL_FBEout$STATION<-"FBE"
I have looked many places and tried many combinations of R-functions and R-lists, but I can't make it work. Quite possible I'm getting it all wrong. I apologize in advance if the question is (too) stupid, but will however be very grateful for any help on the matter.
Pls. notice that I, in the end, want 44 different data-frames created:
1) dataGL_FLIin
2) dataGL_FBEout
3) Etc. ...
ADDED: 2 STATION 2 DIRECTIONS EXAMPLE OF MY PROBLEM
'The one data frame I have'
Date<-c("01-01-15 04:00","01-01-15 04:20","01-01-15 04:40")
FLIin<-c(96,39,72)
FLIout<-c(173,147,103)
FBEin<-c(96,116,166)
FBEout<-c(32,53,120)
dataGL_all<-data.frame(Date, FLIin, FLIout, FBEin, FBEout)
'The four data frames I would like'
GL_antal<-c(96,39,72)
Station<-("FLI")
Dir<-("IN")
dataGL_FLIin<-data.frame(Date, Station, Dir, GL_antal)
GL_antal<-c(173,147,103)
Station<-("FLI")
Dir<-("OUT")
dataGL_FLIout<-data.frame(Date, Station, Dir, GL_antal)
GL_antal<-c(96,116,166)
Station<-("FBE")
Dir<-("IN")
dataGL_FBEin<-data.frame(Date, Station, Dir, GL_antal)
GL_antal<-c(32,53,120)
Station<-("FBE")
Dir<-("OUT")
dataGL_FBEout<-data.frame(Date, Station, Dir, GL_antal)
Thanks,
lars

Answer 1

With your example, it is now clearer what you want and I give it a second try. I use dataGL_all as defined in your question and the define
stations <- rep(c("FLI","FBE"),each=2)
directions <- rep(c("in","out"),times=length(stations)/2)
You could also extract the stations and directions from your data frame. Using your example, the following would work
stations <- substr(names(dataGL_all)[-1],1,3)
directions <- substr(names(dataGL_all)[-1],4,6)
Then, I define the function that will work on the data:
dataGLfun <- function(station,direction) {
name <- paste0(station,direction)
dataGL <- dataGL_all[,c("Date", name)]
names(dataGL)[names(dataGL)==name] <- 'GL_Antal'
dataGL$DIR<-direction
dataGL$STATION<-station
dataGL
}
And now I apply this function to all stations with both directions:
dataGL <- mapply(dataGLfun,stations,directions,SIMPLIFY=FALSE)
names(dataGL) <- paste0(stations,directions)
Now, you can get the data frames for each combination of station and direction. For instance, the two examples in your question, you get with dataGL$FLIin and dataGL$FBEout. The reason that there is a $ instead of a _ is that I did not actually create a separate variable for each data frame. Instead, I created a list, where each element of the list is one of the data frames. This has the advantage that it will be easier to do something to all the data frames later. With your solution, you would have to type all the various variable names, but if the data frames are in a list, you can work with them using functions like lapply.
If you prefer to have many different variables, you could do the following
for (i in seq_along(stations)) {
assign(paste0("dataGL_",stations[i],directions[i]), dataGLfun(stations[i],directions[i]))
}
However, in my opinion, this is not how you should solve this problem in R.