The beaver1 and beaver2 datasets contain body temperatures of two beavers. Add a column named id to the beaver1 dataset where the value is always 1. Similarly, add an id column to beaver2 with value 2. Vertically concatenate both data frames and call this object both_beavers. Find the subset where either beaver is active and call this subset active.

(from: Cotton, 2013, Learning R, O’Reilly)