Adding data frames as list elements (using for loop) - r

Question

I have in my environment a series of data frames called EOG. There is one for each year between 2006 and 2012. Like, EOG2006, EOG2007...EOG2012. I would like to add them as elements of a list.
First, I am trying to know if this is possible. I read the official R guide and a couple of R programming manuals but I didn't find explicit examples about that.
Second, I would like to do this using a for loop. Unfortunately, the code I used to do the job is wrong and I am going crazy to fix it.
for (j in 2006:2012){
z<-j
sEOG<-paste("EOG", z, sep="")
dEOG<-get(paste("EOG", z, sep=""))
lsEOG<-list()
lsEOG[[sEOG]]<-dEOG
}
This returns a list with one single element. Where is the mistake?

Answer 1

You keep reinitializing the list inside the loop. You need to move lsEOG<-list() outside the for loop.
lsEOG<-list()
for (j in 2006:2012){
z <- j
sEOG <- paste("EOG", z, sep="")
dEOG <- get(paste("EOG", z, sep=""))
lsEOG[[sEOG]] <-dEOG
}
Also, you can use j directly in the paste functions:
sEOG <- paste("EOG", j, sep="")

Answer 2

I had the same question, but felt that the OP's initial code was a bit opaque for R beginners. So, here is perhaps a bit clearer example of how to create data frames in a loop and add them to a list which I just now figured out by playing around in the R shell:
> dfList <- list() ## create empty list
>
> for ( i in 1:5 ) {
+ x <- rnorm( 4 )
+ y <- sin( x )
+ dfList[[i]] <- data.frame( x, y ) ## create and add new data frame
+ }
>
> length( dfList ) ## 5 data frames in list
[1] 5
>
> dfList[[1]] ## print 1st data frame
x y
1 -0.3782376 -0.3692832
2 -1.3581489 -0.9774756
3 1.2175467 0.9382535
4 -0.7544750 -0.6849062
>
> dfList[[2]] ## print 2nd data frame
x y
1 -0.1211670 -0.1208707
2 -1.5318212 -0.9992406
3 0.8790863 0.7701564
4 1.4014124 0.9856888
>
> dfList[[2]][4,2] ## in 2nd data frame, print element in row 4 column 2
[1] 0.9856888
>
For R beginners like me, note that double brackets are required to access the ith data frame. Basically, double brackets are used for lists while single brackets are used for vectors.

Answer 3

If the data frames are saved as an object you can find them by apropos("EOG", ignore.case=FALSE) and them with a loop store them in the list:
list.EOG<- apropos("EOG", ignore.case=FALSE) #Find the objects with case sensitive
lsEOG<-NULL #Creates the object to full fill in the list
for (j in 1:length(list.EOG)){
lsEOG[i]<-get(list.EOG[i]) #Add the data.frame to each element of the list
}
to add the name of each one to the list you can use:
names(lsEOG, "names")<-list.EOG