When working with data imported from SPSS I need to access value.labels attribute of some variables.
The names of these variables I get as strings. The only way to pass the variable name (as string) to attr which I have found is through get() but it is very very slow. The situation is quite simple so there is probably a better way how to do it.
The example is artificial but the size (number of variables) is similar to what I work with in real. I also need the data.table in the real situation.
library(data.table)
id <- c(1:4000)
x <- sample(1:3, 4000, replace=T)
dv<-c(id,x)
df<-data.frame(t(dv))
dt<-data.table(df)
attr(dt$X1,"value.labels")<-c("first","second","third")
#direct approach is fast
pm<-proc.time()
attr(dt[,X1],"value.labels")
proc.time() - pm
user system elapsed
0.00 0.04 0.03
#using variable name as a string is slow
pm<-proc.time()
attr(dt[,get("X1")],"value.labels")
proc.time() - pm
user system elapsed
0.85 0.03 0.89
The get() solution is incredibly slow but it works.
attr(dt[,"X1", with=FALSE],"value.labels")
NULL
attr(dt[,match("X1",names(dt)),with=FALSE],"value.labels")
NULL
Does not work.
