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I am trying to understand how to use the package mmap to access large csv files. More precisely, I'd like to Create a mmap object from a csv file with mmap.csv() ; Save the file created by mmap.csv() containing the data in binary format; Be able to "map the binary data back to R" using the function mmap() . Achieving 1. and 2. is easy: just use mmap.cv() and save the tempfile() that contains the binary data, or modify mmap.cv() to accept an extra parameter as output file (and modify the line tmpstruct <- tempfile() accordingly). What I am having trouble with is 3. In particular, I need to construct a C-struct for the records in the binary data from the mmap object. Here is a simple reproducible example: # create mmap object with its file library(mmap) data(cars) m <- as.mmap(cars, file="cars.Rmap") colnames(m) <- colnames(cars) str(m) munmap(m) The information from str() can be used to construct the C-struct record.struct that allows mapping the binary file cars.Rmap via the function mmap. > str(m) <mmap:temp.Rmap> (struct) struct [1:50, 1:2] 4 ... data :<externalptr> bytes : num 400 filedesc : Named int 27 - attr(*, "names")= chr "temp.Rmap" storage.mode :List of 2 $ speed:Classes 'Ctype', 'int' atomic (0) .. ..- attr(*, "bytes")= int 4 .. ..- attr(*, "signed")= int 1 $ dist :Classes 'Ctype', 'int' atomic (0) .. ..- attr(*, "bytes")= int 4 .. ..- attr(*, "signed")= int 1 - attr(*, "bytes")= int 8 - attr(*, "offset")= int [1:2] 0 4 - attr(*, "signed")= logi NA - attr(*, "class")= chr [1:2] "Ctype" "struct" pagesize : num 4096 dim :NULL In this case, we need two 4-byte integers:</

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