问题
I have a IMDB dataset and trying to make a boxplot of a film's ratings.
I've successfully loaded the dataset and tried to make the boxplot but it produced a really weird result.
It looked as it tried to make a boxplot for all the films and not just the one selected.
boxplot(rating ~ title, data=imdb[imdb$title == "Top Gun (1986)", ])
The graph produced:
As you can see the y axis looks as if it contained films that aren't in the filtered dataset at all (I selected those via title).
回答1:
Factors retain their levels even after subsetting, you can drop those that are unused with droplevels:
boxplot(rating ~ title, data=droplevels(imdb[imdb$title == "Top Gun (1986)", ]))
来源：https://stackoverflow.com/questions/40226097/boxplot-sees-values-that-arent-there