[r] Error in eval(expr, envir, enclos) : object not found

I cannot understand what is going wrong here.

data.train <- read.table("Assign2.WineComplete.csv",sep=",",header=T)
# Building decision tree
Train <- data.frame(residual.sugar=data.train$residual.sugar,
                total.sulfur.dioxide=data.train$total.sulfur.dioxide, 
                alcohol=data.train$alcohol,
                quality=data.train$quality)
Pre <- as.formula("pre ~ quality")

fit <- rpart(Pre, method="class",data=Train)

I am getting the following error :

Error in eval(expr, envir, enclos) : object 'pre' not found

I think I got what I was looking for..

data.train <- read.table("Assign2.WineComplete.csv",sep=",",header=T)
fit <- rpart(quality ~ ., method="class",data=data.train)
plot(fit)
text(fit, use.n=TRUE)
summary(fit)

This can happen if you don't attach your dataset.

i use colname(train) = paste("A", colname(train)) and it turns out to the same problem as yours.

I finally figure out that randomForest is more stingy than rpart, it can't recognize the colname with space, comma or other specific punctuation.

paste function will prepend "A" and " " as seperator with each colname. so we need to avert the space and use this sentence instead:

colname(train) = paste("A", colname(train), sep = "")

this will prepend string without space.