R passing data.table parameters through function calls -

so if have data.table defined as:

> dt <- data.table (x=c(1,2,3,4), y=c("y","n","y","m"), z=c("pickle",3,8,"egg"))      > dt         x   y        z      1:  1   y   pickle     2:  2   n        3     3:  3   y        8     4:  4   m      egg 

and variable

    fn <- "z" 

i can pull column data.table following:

    > dt[,fn, with=false] 

what don't know how data.table equivalent of following:

    > factorfunction <- function(df, fn) {       df[,fn] <- as.factor(df[,fn])       return(df)      } 

if set fn="x" , call factorfunction(data.frame(dt),fn) works fine.

so try data.table, doesn't work

    > factorfunction <- function(dt, fn) {       dt[,fn, with=false] <- as.factor(dt[,fn, with=false])       return(dt)      } 

error in sort.list(y) : 'x' must atomic 'sort.list' have called 'sort' on list?

you can try

 dt[,(fn):= factor(.sd[[1l]]),.sdcols=fn] 

if there multiple columns, use lapply(.sd, factor)

wrapping in function

factorfunction <- function(df, fn) {  df[, (fn):= factor(.sd[[1l]]), .sdcols=fn]  }   str(factorfunction(dt, fn))  #classes ‘data.table’ , 'data.frame':    4 obs. of  3 variables:  #$ x: num  1 2 3 4  #$ y: chr  "y" "n" "y" "m"  #$ z: factor w/ 4 levels "3","8","egg",..: 4 1 2 3