Reclassify select columns in Data Table

Question

I wish to change the class of selected variables in a data table, using a vectorized operation. I am new to the data.table syntax, and am trying to learn as much as possible. I

Answer 1

You could avoid the overhead of the construction of .SD within j by using set

for(j in index) set(data, j =j ,value = as.character(data[[j]]))

Answer 2

You just need to use .SDcols with your index vector (I learnt that today!), but that will just return a data table with the reclassed columns. @dickoa 's answer is what you are looking for.

data <- data[, lapply(.SD, as.character) , .SDcols = index ]
sapply(data , class)
        id      height      weight 
"character" "character" "character" 

Answer 3

I think that @SimonO101 did most of the Job

data[, names(data)[index] := lapply(.SD, as.character) , .SDcols = index ]

You can just use the := magic