Ruby：将值写入CSV文件中的特定位置

Question

I'm still fairly new to coding and I'm trying to learn about manipulating CSV files.

The code below opens a specified CSV file, goes to each url in the CSV file in column B (header = url), and finds the price on the webpage.

Example data from CSV file:

Store,URL,Price
Walmart,http://www.walmart.com/ip/HP-11.6-Stream-Laptop-PC-with-Intel-Celeron-Processor-2GB-Memory-32GB-Hard-Drive-Windows-8.1-and-Microsoft-Office-365-Personal-1-yr-subscription/39073484
Walmart,http://www.walmart.com/ip/Nextbook-10.1-Intel-Quad-Core-2-In-1-Detachable-Windows-8.1-Tablet/39092206
Walmart,http://www.walmart.com/ip/Nextbook-10.1-Intel-Quad-Core-2-In-1-Detachable-Windows-8.1-Tablet/39092206

I'm having trouble writing that price to the adjacent column C (header = price) in the same CSV.

require 'nokogiri'
require 'open-uri'
require 'csv'

contents = CSV.open "mp_lookup.csv", headers: true, header_converters: :symbol
contents.each do |row|
  row_url = row[:url]
  goto_url = Nokogiri::HTML(open(row_url))
  new_price = goto_url.css('meta[itemprop="price"]')[0]['content']

#----
#In this section, I'm looking to write the value of new_price to the 3rd column in the same CSV file

#----

end

In the past, I've been able to use:

in_file = open("mp_lookup.csv", 'w')
in_file.write(new_price)

But this doesn't seem to work in this situation.

Any help is appreciated!

Answer 1

The simple answer is that you can refer to the :price column in the CSV file, just like you refer to the :url column. Try this code to set the price in the CSV object in memory:

row[:price] = new_price

After you've read through all of the records, you'll want to save the CSV file again. You can save it to any filename, but we'll simply overwrite the previous file in this example:

CSV.open("mp_lookup.csv", "wb") do |csv|
  contents.each do |row|
      csv << row
  end
end

In a real production environment, you'd want to be more fault tolerant than this, and preserve the original file until the end of the process. However, this shows how to update the values in the price column for each row, and then save the changes to a file.