[R] contrasts can be applied only to factors with 2 or more levels

[javed khan]

I am using the folowing code and it give me the error message like

" contrasts can be applied only to factors with 2 or more levels".

What could be the problem

d=read.csv("Result.csv")
index <- createDataPartition(log10(d$Results), p = .70,list = FALSE)
tr <- d[index, ]
ts <- d[-index, ]
index_2 <- createFolds(log10(tr$Results), returnTrain = TRUE, list = TRUE)
ctrl <- trainControl(method = "cv", index = index_2)

set.seed(30218)

grid_search <- train(log10(Results) ~ ., data = tr,
                     method = "svmRadial",

                     tuneLength = 8,
                     metric = "MAE",
                     preProc = c("center", "scale", "zv"),
                     trControl = ctrl)

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