\begin{Schunk}
\begin{Sinput}
 str(grades)
\end{Sinput}
\begin{Soutput}
'data.frame':	7 obs. of  9 variables:
 $ namelast : chr  "Potter" "Granger" "Weasley" "Malfoy" ...
 $ namefirst: chr  "Harry" "Hermoine" "Ron" "Draco" ...
 $ id       : num  453345 942832 342234 666666 234252 ...
 $ hw1      : num  8 7 9 8 6 5 8
 $ hw2      : num  7 NA 8 4 8 9 7
 $ hw3      : chr  "P" "P" "F" "P" ...
 $ mterm    : num  84 101 78 66 87 81 84
 $ fin      : num  77 999 88 85 77 79 66
 $ grade    : chr  "B" "A+" "B-" "C+" ...
\end{Soutput}
\end{Schunk}
