How do I create a copy of some columns of a CSV file in Ruby with different data in one column?

Solution 1:

As mikeb pointed out, there are the docs - http://ruby-doc.org/stdlib-1.9.3/libdoc/csv/rdoc/CSV.html - Or you can follow along with the examples below (all are tested and working):

To create a new file:

In this file we'll have two rows, a header row and data row, very simple CSV:

require "csv"
CSV.open("file.csv", "wb") do |csv|
  csv << ["animal", "count", "price"]
  csv << ["fox", "1", "$90.00"]
end

result, a file called "file.csv" with the following:

animal,count,price
fox,1,$90.00

How to append data to a CSV

Almost the same formula as above only instead of using "wb" mode, we'll use "a+" mode. For more information on these see this stack overflow answer: What are the Ruby File.open modes and options?

CSV.open("file.csv", "a+") do |csv|
  csv << ["cow", "3","2500"]
end

Now when we open our file.csv we have:

animal,count,price
fox,1,$90.00
cow,3,2500

Read from our CSV file

Now you know how to copy and to write to a file, to read a CSV and therefore grab the data for manipulation you just do:

CSV.foreach("file.csv") do |row|
  puts row #first row would be ["animal", "count", "price"] - etc.
end

Of course, this is like one of like a hundred different ways you can pull info from a CSV using this gem. For more info, I suggest visiting the docs now that you have a primer: http://ruby-doc.org/stdlib-1.9.3/libdoc/csv/rdoc/CSV.html

Solution 2:

Have you seen Ruby's CSV class? It seems pretty comprehensive. Check it out here: http://ruby-doc.org/stdlib-1.9.3/libdoc/csv/rdoc/CSV.html