How do i parse columns in a CSV File in Ruby and store it as an array

Question

lets say we have the following csv file:

Date,Av,Sec,128,440,1024,Mixed,,rule,sn,version

6/30/2010,3.40,343,352.0,1245.8,3471.1,650.7,Mbps,on,s-2.8.6-38,4.9.1-229,,vs. 342,-0.26%,-0.91%,1.51%,-0.97% 6/24/2010,3.40,342,352.9,1257.2,3419.5,657.1,Mbps,on,s-2.8.6-38,4.9.1-229,,vs. 341,0.23%,0.50%,-1.34%,0.67% 6/17/2010,3.40,341,352.1,1251.0,3466.1,652.7,Mbps,on,s-2.8.6-38,4.9.1-229,,vs. 340,7.77%,5.32%,9.04%,1.71% 6/14/2010,3.40,340,326.7,1187.8,3178.7,641.7,Mbps,on,s-2.8.6-38,4.9.1-229,,vs. 339,-0.88%,-0.34%,-0.95%,0.05% 6/11/2010,3.40,339,329.6,1191.9,3209.2,641.4,Mbps,on,s-2.8.6-38,4.9.1-229,,vs. 338,0.58%,0.51%,-1.83%,0.99% 6/11/2010,3.40,338,327.7,1185.8,3269.1,635.1,Mbps,on,s-2.8.6-38,4.9.1-229,,vs. 335,-0.40%,-0.44%,1.46%,-1.96% 6/11/2010,3.40,335,329.0,1191.0,3221.9,647.8,Mbps,on,s-2.8.6-38,4.9.1-229,,vs. 333,-6.83%,-4.70%,-7.04%,-0.32% 6/11/2010,3.40,333,353.1,1249.8,3465.8,649.9,Mbps,on,s-2.8.6-38,4.9.1-229,,vs. 332,2.53%,2.02%,1.71%,2.14%

and i want to parse 4, 5 6 and 7th column and have 4 arrays, on which i can do operations like create a line graph against time, etc

Answer 1

You need the Ruby CSV module which ships with Ruby. Example:

require 'csv'
require 'pp'

file = File.open( 'bar.csv' )
CSV::Reader.create( file ).each do |row|
  pp row[4..7]
end

Answer 2

why reinvent the wheel!

Use plugin fastercsv or csv

Answer 3

You are spoiled for choice in parsing CSVs with Ruby, as there are options included in the standard lib, as well as easy home-brewed methods or Open Source libs.

You can start with the examples on this page, and that should point you in the direction for digging deeper.