I have a data frame called my.df which contains two columns, month and temperature. The temperature column contains the daily maximum temperature in Kelowna for every day of a single year, and the month column contains the corresponding months. That is, the rst few rows of my.df are "January" 5 "January" 2 "January" -1 and so on. I would like to calculate all of the monthly average temperatures. To do this, | type (temperature ~ month), data = , FUN = If, instead, I want to construct a data frame that consists of only the records where the temperature is less than 2, | type (my.df, temperature