data <- data.frame("v1" = runif(10, 0, 10), "v2" = runif(10, 0 ,10), "v3" = runif(10, 0 ,10), "v4" = rep("some_charchter", 10))

data$sum <- rowSums(data[,1:3])

data <- data.frame("v1" = runif(10, 0, 10), "v2" = runif(10, 0 ,10), "v3" = runif(10, 0 ,10), "v4" = rep("some_charchter", 10)) %>%
  mutate(sum = rowSums())