The mutate() function from dplyr is extremely useful one for adding new columns to a dataframe based on computations from existing columns. It is a vectorized function, though, and is often misunderstood as working row-wise when it actually works column-wise, that is, on whole vectors with R's built-in recycling. This behavior can often be confusing for those looking to use mutate() on non-trivial examples or with custom functions, so, in this recipe, we're going to examine how mutate() actually behaves in certain situations, with the hope that this will be enlightening.