A setcols function for data.table

mutate_cols_DT.R

# I love data.table, but I find the syntax for "mutating" columns a little clunky for such a common task
# I wonder if it would be useful to have a setcols() function? 
# Takes advantage of data.table's pass-by-reference

library(data.table)
setcols <- function(my_dt, cols, my_fun) {
  # validate inputs
  stopifnot('data.table' %in% class(my_dt),
            'character' == class(cols),
            'function' == class(my_fun))
  # apply my_fun to cols in my_dt
  for(j in cols) set(my_dt, j = j, value = my_fun(my_dt[[j]]))
}

# Now you can do things like this.
# ...given a data.table of mixed types
dat <- data.table(letters = c('a', 'b', 'c', 'd', 'e'),
                  fruits  = c('apple', 'banana', 'carrot', 'durian', 'elderberry'),
                  num1    = rnorm(5),
                  num2    = seq(10, 50, 10))

# ...change some data types
setcols(dat, c('letters', 'fruits'), as.factor)

# ...transform some numbers
setcols(dat, c('num1', 'num2'), function(x) x*2 + 5)

# This simple wrapper seems to stay idiomatic to data.table, which already has 
# functions setDT and setnames which modify the data.table passed to them

Not sure setcols is the right name. Maybe mutate_cols but that's dplyr talk. Seems like data.table needs something in the set[...] family