2.7 Quiz answers

1. You must quote non-syntactic names with backticks: `: for example, the variables 1, 2, and 3.

   df <- data.frame(runif(3), runif(3))
   names(df) <- c(1, 2)
   
   df$`3` <- df$`1` + df$`2`

2. It occupies about 8 MB.

   x <- runif(1e6)
   y <- list(x, x, x)
   obj_size(y)
   #> 8,000,128 B

3. a is copied when b is modified, b[[1]] <- 10.