Condense a data frame.
condense(data, variables, fun, ...)data frame
variables to condense over
aggregating function, may multiple values
further arguments passed on to aggregating function
Works very much like by, but keeps data in original data frame format. Results column is a list, so that each cell may contain an object or a vector etc. Assumes data is in molten format. Aggregating function must return the same number of arguments for all input.