title: Removing rows based on how often they a value occurs
body: <p>I am working with the Supreme Court Database, a very large data set. I am making new data frames for each natural court, but am only interested in cases in which all 9 justices have voted. Each justice's vote is a row in the data set where only the justice name and vote values are different. Is there a way to eliminate all case names that occur less than 9 times (ie. case names that occur in less than nine consecutive rows)?</p>