##### Removing constant features
cat("n## Removing the constants features.n")
for (f in names(train)) {
  if (length(unique(train[[f]])) == 1) {
    cat(f, "is constant in train. We delete it.n")
    train[[f]] <- NULL
    test[[f]] <- NULL
  }
}

##### Removing identical features
features_pair <- combn(names(train), 2, simplify = F)
toRemove <- c()
for(pair in features_pair) {
  f1 <- pair[1]
  f2 <- pair[2]

  if (!(f1 %in% toRemove) & !(f2 %in% toRemove)) {
    if (all(train[[f1]] == train[[f2]])) {
      cat(f1, "and", f2, "are equals.n")
      toRemove <- c(toRemove, f2)
    }
  }
}