\begin{Schunk}
\begin{Sinput}
 set.seed(234234)
 titanic <- titanic0
 titanic$sex[sample(nrow(titanic), 400)] <- NA 
 titanic$pclass[sample(nrow(titanic), 400)] <- NA 
 titanic$survived[sample(nrow(titanic), 400)] <- NA
\end{Sinput}
\end{Schunk}
