Some data:
require(data.table)
set.seed(123)
DT <- data.table(factor = c("a", "b", "c"), num = rpois(6, 30))
DT[["factor"]] <- factor(DT[["factor"]])
levels(DT[["factor"]])
# [1] "a" "b" "c"
get_levels <- function(data, factor){
data = substitute(data)
factor = substitute(factor)
factor_levels = levels(data[["factor"]])
print(factor_levels)
}
get_levels(DT, factor)
get_levels2 <- function(data, factor){
data = substitute(data)
factor = substitute(factor)
factor_levels = levels(data[[factor]])
print(factor_levels)
}
get_levels2(DT, factor)
get_levels3 <- function(data, factor){
data = substitute(data)
factor = substitute(factor)
factor_levels = levels(eval(data[[deparse(factor)]]))
print(factor_levels)
}
get_levels3(DT, factor)
Error in data[["factor"]] : object of type 'symbol' is not subsettable
Error in data[[deparse(factor)]] :
object of type 'symbol' is not subsettable
substitute
deparse
eval
parse
If you're not experienced with R (or programming in general) avoid substitute
, deparse
, eval
, etc. They are rarely necessary.
DT <- data.table(f = c("a", "b", "c"), num = rpois(6, 30))
DT[["f"]] <- factor(DT[["f"]])
get_levels <- function(data,fac){
levels(data[[fac]])
}
get_levels(DT,'f')
And don't call your column factor
. That's a function, and it's just confusing.