could not find function "as.data.frame.ffdf"

Question

I'm following the guide Big Data Analytics with R. But the as.data.frame.ffdf function seems to be missing.

Does anyone have an idea? Or is there any alternative solution?

Here's sample code:

# Data were downloaded from Bureau of Transportation Statistics:
# http://www.transtats.bts.gov/DL_SelectFields.asp?Table_ID=236&DB_Short_Name=On-Time
library(Hmisc);library(ff);library(ffbase)
flights.ff <- read.table.ffdf(file = "flights_sep_oct15.txt",
                              sep = ",", VERBOSE = T,
                              header = T, next.rows = 100000,
                              colClasses = NA)
describe(as.data.frame.ffdf(flights.ff$DISTANCE))