Box-plot generation inhibits later commands

[drewbo]

If running the code linearly, this bit of code to make the 'Title" column a factor (so we can make a box-plot),

> df.train$Title <- factor(df.train$Title,
                       c("Capt","Col","Major","Sir","Lady","Rev",
                       "Dr","Don","Jonkheer","the Countess","Mrs",
                       "Ms","Mr","Mme","Mlle","Miss","Master"))

will later cause an error when trying to reassign the grouped titles:

> df.train$Title <- changeTitles(df.train, 
                             c("Capt", "Col", "Don", "Dr", 
                               "Jonkheer", "Lady", "Major", 
                               "Rev", "Sir"),
                             "Noble")
In `[<-.factor`(`*tmp*`, which(data$Title == honorific), value = c(13L,  :
invalid factor level, NA generated