dplyr: Evaluate the sum of variables whose names are in a vector

Question

I need to programmatically add multiple variables whose name is in a vector. For example, given this vector:

myvars <- c("Expectation", "Interesting", "Useful", "OralPresentation")

how can I write the following expression using the previous vector?

df %>%
  mutate(TotalEvaluation = Expectation + Interesting + Useful + OralPresentation)

Answer 1

We can use rowSums after subsetting the columns of the dataset

library(dplyr)
df %>% 
      mutate(TotalEvaluation = rowSums(.[myvars]))