Question

What I’m doing is this: have one file as input, another as output. I chose a random line in the input, put it in the output, and then delete it.

Now, I’ve iterated over the file and am on the line I want. I’ve copied it to the output file. Is there a way to delete it? I’m doing something like this:

for i in 0..number_of_lines_to_remove
    line = rand(lines_in_file-2) + 1 #not removing the first line
    counter = 0
    IO.foreach("input.csv", "r") { |current_line|
      if counter == line
        File.open("output.csv", "a") { |output|
          output.write(current_line)
        }
      end
      counter += 1
    }
end

So, I have current_line, but I’m not sure how to remove it from the source file.

Answer 1

Array.delete_at might do. Given an index, it removes the object at that index, returning the object.

input.csv:

one,1
two,2
three,3

Program:

#!/usr/bin/ruby1.8

lines = File.readlines('/tmp/input.csv')
File.open('/tmp/output.csv', 'a') do |file|
  file.write(lines.delete_at(rand(lines.size)))
end
p lines    # ["two,2\n", "three,3\n"]

output.csv:

one,1