> # base
> dat <- data.frame(a = c(10, 11, 12),
+                   b = c(4, 5, 6),
+                   colour = c("blue", "green", "yellow"),
+                   stringsAsFactors = FALSE)
> dat$c <- 2 * dat$a
> dat$sum <- dat$a + dat$b
>
> # dplyr
> dat <- data_frame(a = c(10, 11, 12),
+                   b = c(4, 5, 6),
+                   colour = c("blue", "green", "yellow")) %>%
+        mutate(c = 2 * a,
+               sum = a + b)