Data Preparation – Part II

This time i will talk about how to deal with large text files in chuncks with R. Just to provide some real data to work with download Airlines data, relative to 1988; from now on i will work with this file.

To work with this data i will use  iterators package. This package allow you pass the file, line by line, or chunck by chunk, without really load all file to memory. As you can feel the idea try this code:

install.packages('iterators')
library(iterators)
con <- bzfile('1988.csv.bz2', 'r')

OK, now you have a connection to your file. Let’s create a iterator:

it <- ireadLines(con, n=1)
nextElem(it)
nextElem(it)

As you can see you are printing line by line. So, you can work with one line, or a chunk of data even with a large file. If you want to read line by line till the end of the file you can use something like this:

tryCatch(expr=nextElem(it), error=function(e) return(FALSE))

that returns a FALSE at the end of the file. This a very useful trick in data preparation with large text files.