Question

How can I read multiple lines at a time from a file in Ruby?

I tried using each_slice(2) and also did: require 'enumerator', but it doesn’t work. I get the following error:

undefined method `each_slice' for #<String:0x877d12c> (NoMethodError)

Answer 1

Both IO and String have a lines enumerator, which you can call each_slice on:

irb(main):004:0> STDIN.lines.each_slice(2).take(2)
a
a
b
c
=> [["a\n", "a\n"], ["b\n", "c\n"]]

Of course you can substitute STDIN with any other IO instance (open file). Demo with a string:

irb(main):005:0> "a\na\nb\nc".lines.each_slice(2).to_a
=> [["a\n", "a\n"], ["b\n", "c"]]

Both of these work in Ruby >= 1.8.7