A few days ago a friend asked me the following question: how to efficiently extract some specific lines from a large text file, possibily compressed by Gzip? He mentioned that he tried some R functions such as read.table(skip = …), but found that reading the data was too slow. Hence he was looking for some alternative ways to extracting the data. This is a common task in preprocessing large data sets, since in data exploration, very often we want to peek at a small subset of the whole data to gain some insights.