Error with my new example

[mstaniak]

Error in contrasts<-(*tmp*, value = contr.funs[1 + isOF[nn]]) : contrasts can be applied only to factors with 2 or more levels

set.seed(17)
faktor <- sample(c(0, 1), 500, prob = c(0.5, 0.5), replace = T)
table(faktor)
set.seed(17)
numeric <- rnorm(500)
set.seed(17)
y <- (-1)^(faktor)*4*numeric + 0.5 + rnorm(500)
set.seed(17)
X <- data.frame(y = y,
                x1 = as.factor(faktor),
                x2 = numeric,
                x3 = runif(500))
library(randomForest)
library(dplyr)
X_train <- sample_frac(X, 0.8)
X_test <- setdiff(X, X_train)

rf_m <- randomForest(y ~., data = X_train, ntree = 1000)
mean((predict(rf_m, X_test[, -1]) - X_test[, 1])^2)
library(DALEX2)

dalex_explainer <- DALEX2::explain(rf_m, data = X_train[, -1])

library(localModel)
lm_explanation_4 <- individual_surrogate_model(dalex_explainer, X[4, -1],
                                               1000, 17, gaussian_kernel)