Reading specific rows of large matrix data file

Question

Suppose I have a gigantic m*n matrix X (that is too big to read into memory) and binary numeric vector V with length m. My objective is to

Answer 1

A viable strategy is to import the CSV file into a database (R supports connections to most of them. Go with MonetDB if you're feeling bleeding edge and speed matters; SQLite or whatever is handy otherwise).

Then you can specify the appropriate subset using SQL and read that into R.