mxnet2.R

#load package
require(mxnet)

#convert target variables into numeric
train[,target := as.numeric(target)-1]
test[,target := as.numeric(target)-1]

#convert train data to matrix
train.x <- data.matrix(train[,-c("target"),with=F])
train.y <- train$target

#convert test data to matrix
test.x <- data.matrix(test[,-c("target"),with=F])
test.y <- test$target

When I convert the target variables into numeric, I get the following warning:
"Warning message:
In eval(expr, envir, enclos) : NAs introduced by coercion"
I checked train and test variables again after that and the whole "target" column is filled with NAs. How can I solve this?
Thanks in advance!