No seed set in section 26.2

[jcornickm]

Since no seed is set in generating the df used in this section, the results each user will get when computing the median for each column will be different from those in the book, which might be a bit confusing. My first reaction when I saw my results didn´t match the book was to find a mistake in my code, and then I realized what was going on. You might want to considering either setting a seed before using rnorm() or warning the reader that their results will not be the same as in the book. Just a suggestion.