Change Headers for Certain Columns in CSV File - ruby

Question

I have a CSV file that I want to change the headers only for certain columns (about 20 of them in my actual file). Here's a sample CSV file:
CSV File
"name","blah_01_blah","foo_1_01_foo","bacon_01_bacon","bacon_02_bacon"
"John","yucky","summer","yum","food"
"Mary","","","cool","sundae"
I have been trying this with a File/IO class, but when it reads the file to do the gsub it removes all of the quotation marks around each string separated by commas. Here's the code I'm using:
Ruby Code
file = 'file.csv'
replacements = {
'blah_01_blah' => 'newblah1',
'foo_01_foo' => 'coolfoo1',
'bacon_01_bacon' => 'goodpig1',
'bacon_01_bacon' => 'goodpig2'
}
matcher = /#{replacements.keys.join('|')}/
outdata = File.read(file).gsub(matcher, replacements)
File.open(file, 'w') do |out|
out << outdata
end
What I end up with is this in the CSV file:
New CSV File
name,blah_01_blah,foo_1_01_foo,bacon_01_bacon,bacon_02_bacon
John,yucky,summer,yum,food
Mary,"","",cool,sundae
It's keeping the quotation marks in fields that are blank, but taking them out around the strings elsewhere. I want to retain those quotation marks in case for some reason a rogue comma ends up in a string somewhere so it doesn't get thrown off. How can I change the headers without losing my quotation marks around the strings?
EDIT - This is what I want the file to look like at the end.
Expected Result CSV File
"name","newblah1","coolfoo1","goodpig1","goodpig2"
"John","yucky","summer","yum","food"
"Mary","","","cool","sundae"
Thanks!

Answer 1

You don’t need to handle CSV at all:
File.write(
file,
File.readlines(file).tap do |lines|
lines.first.gsub!(matcher, replacements)
end.join
)
File#readlines.
The trick here is we actually deal with the first line only, as with plain text.

Answer 2

Let's first create the input CSV file.
text =<<_
"name","blah_01_blah","foo_1_01_foo","bacon_01_bacon","bacon_02_bacon"
"John","yucky","summer","yum","food"
"Mary","","","cool","sundae"
_
file_in = 'file_in.csv'
file_out = 'file_out.csv'
File.write(file_in, text)
#=> 137
Here is the replacements hash, which I simplified slightly.
replacements = {'blah_01_blah'=>'newblah1', 'foo_01_foo'=>'coolfoo1',
'bacon_01_bacon'=>'goodpig1'}
The first task is to modify this hash so that if it has no key k, replacements[k] will return k. For this we use the method Hash#default_proc=.
replacements.default_proc = ->(_,k) { k }
Here are two examples of how this hash is used.
replacements['bacon_01_bacon']
#=> "goodpig1"
replacements['name']
#=> "name"`
The latter follows because replacements has no key 'name'.
The code is as follows.
require 'csv'
f_in = CSV.read(file_in, headers:true)
CSV.open(file_out, 'w') do |csv_out|
csv_out << replacements.values_at(*f_in.headers)
f_in.each { |row| csv_out << row }
end
#=> #<CSV::Table mode:col_or_row row_count:3>
Note that
f_in.headers
#=> ["name", "blah_01_blah", "foo_1_01_foo", "bacon_01_bacon", "bacon_02_bacon"]
Let's look at the output file.
puts File.read(file_out)
prints
name,newblah1,foo_1_01_foo,goodpig1,bacon_02_bacon
John,yucky,summer,yum,food
Mary,"","",cool,sundae