Why the ffdf object is so large?

I use read.csv.ffdf from ff package to load a 830MB CSV file, which is about 8800000 rows and 19 columns: 

library(ff)  library(ffbase)  green_2018_ff <- read.csv.ffdf("green_2018.csv", header = TRUE)  

But when I check the the size of green_2018_ff using object_size from pryr package, the object is about 1.13GB in memory:

library(pryr)  object_size(green_2018_ff)  #1.13GB  

I used to consider that the ffdf is only a memory mapping object, it should be very small in memory, much smaller than the origin CSV. Is there anything wrong with my code or data? Thanks. 

https://stackoverflow.com/questions/65929763/why-the-ffdf-object-is-so-large January 28, 2021 at 09:28AM