Having trouble putting my header back on my CSV file - arrays

Question

Here is my code:
require 'CSV'
contents = CSV.read('/Users/namename/Desktop/test.csv')
arr = []
first_row = contents[0]
contents.shift
contents.each do |row|
if row[12].to_s =~ /PO Box/i or row[12].to_s =~ /^[[:digit:]]/
#File.open('out.csv','a').puts('"'+row.join('","')+'"')
arr << row
else
row[12], row[13] = row[13], row[12]
#File.open('out.csv','a').puts('"'+row.join('","')+'"')
arr << row
end
end
arr.unshift(first_row)
arr.each do |row|
File.open('out.csv', 'a').puts('"' + row.join('","') + '"')
end
First I .shift so that my header fields don't catch the pattern (and ultimately swap) in the first conditional of the first .each loop. Then I conditionally swap cell values that match the pattern, and then store the correctly shifted values in an array. After this, I .unshift to attempt to put back my header fields I stored in first_row, but when I view the resulting out.csv file I get all my headers in the middle. Why?
Example data:
https://gist.github.com/anonymous/e1017d3ba81634d9e1227e7fe49536cb

Answer 1

The root of your problem is that you're not using the features provided by the CSV module.
First, CSV.read takes a :headers option that will catch the headers for you so you don't have to worry about them and, as a bonus, lets you access fields by header name instead of numeric index (handy if the CSV fields' order is changed). With the :headers option, CSV.read returns a CSV::Table object, which has another benefit I'll discuss in a moment.
Second, you're generating your own faux-CSV output instead of letting the CSV module do it. This, in particular, is needless and dangerous:
...puts('"' + row.join('","') + '"')
If any of your column values has quotation marks or newlines, which need to be escaped, this will fail, badly. You could use CSV.generate_line(row) instead, but you don't need to if you've used the headers: option above. Like I said, it returns a CSV::Table object, which has a to_csv method, and that method accepts a :force_quotes option. That will quote every field just like you want—and, more importantly, safely.
Armed with the above knowledge, the code becomes much saner:
require "csv"
contents = CSV.read('/Users/namename/Desktop/test.csv', headers: true)
contents.each do |row|
next unless row["DetailActiveAddressLine1"] =~ /PO Box|^[[:digit:]]/i
row["DetailActiveAddressLine1"], row["DetailActiveAddressLine2"] =
row["DetailActiveAddressLine2"], row["DetailActiveAddressLine1"]
end
File.open('out.csv', 'a') do |file|
file.write(contents.to_csv(force_quotes: true))
end
If you'd like, you can see a version of the code in action (without file access, of course) on Ideone: http://ideone.com/IkdCpb