I have a Ruby script that goes through a CSV, determines some information, and then puts out a resulting CSV file. In Python, I'm able to open both my source file and my results file with DictReader and DictWriter respectively and write rows as dictionaries, where keys are the file header values. It doesn't appear that there is a manageable way to do this in Ruby, but I'm hoping somebody can point me to a better solution than storing all of my result hashes in an array and writing them after the fact.
The standard library "CSV" gives rows hash-like behavior when headers are enabled.
require 'csv'
CSV.open("file.csv", "wb") do |csv_out|
CSV.foreach("test.csv", headers: true) do |row|
row["header2"].upcase! # hashlike behaviour
row["new_header"] = 12 # add a new column
csv_out << row
end
end
(test.csv has a header1, a header2 and some random comma separated string lines.)
Related
I have some data I was writing from one CSV to another CSV because I need to do some data manipulation.
I noticed the CSV library has some default converters that are taking my values that look like dates and parsing those into new date strings.
I was wondering if I could remove all converters? I tried using my custom converter, but no matter what I do it seems that the dates keep getting parsed.
Here is my code simplified:
require 'csv'
CSV::Converters[:my_converter] = lambda do |value|
value
end
CSV.open('new-data.csv', 'w') do |csv|
data = CSV.read('original-data.csv', :converters => [:my_converter]).each do |row|
csv << row
end
end
The value 9/30/14 0:00 is getting changed to 9/30/2014 0:00, for example.
Are you sure that your CSV file doesn't actually contain the 4-digit year? Try looking at puts File.read('original-data.csv')
When I tried this on Ruby 2.1.8, it didn't change the value
require 'csv'
my_csv_data = 'hello,"9/30/14 0:00",world'
CSV.new(my_csv_data).each do |row|
puts row.inspect # prints ["hello", "9/30/14 0:00", "world"], as expected
end
CSV files are not parsed and converted into objects, the data in the fields is returned as a string. Always. This behavior is different than YAML or JSON, which do convert back to their base types.
Consider this:
require 'csv'
CSV.parse("1,10/1/14,foo") # => [["1", "10/1/14", "foo"]]
All values are strings.
csv = ["foo", 'bar', 1, Date.new(2014, 10, 1)].to_csv # => "foo,bar,1,2014-10-01\n"
Converting an array containing native Ruby objects results in a string of comma-delimited values.
CSV.parse(csv) # => [["foo", "bar", "1", "2014-10-01"]]
Reparsing that string returns the string versions but doesn't attempt to return them to their original types as CSV doesn't have a way of knowing what those were. The developer (you) has to know and do that.
The end-result of all that is that CSV won't change a year from '14' to '2014'. It doesn't know that it's a date, and, because it's not CSV's place to convert to objects, it only splits the fields appropriately and passes the information on to be massaged by the developer.
Though it seems far more common for people to use the Ruby CSV class methods, I have an occasion to use a CSV instance, but it seams completely uncooperative.
What I'd like to do is create a CSV instance, add some rows to it, then be able to retrieve all those rows and write them to a file. Sadly, the following code doesn't work as I would like at all.
require 'csv'
csv = CSV.new('', headers: ['name', 'age'])
csv.read # Apparently I need to do this so that the headers are actually read in.
csv.add_row(['john', '22'])
csv.add_row(['jane', '24'])
csv.read
csv.to_a
csv.to_s
All I want to be able to retrieve the information I put into the csv and then write that to a file, but I can't seem to do that :/
What am I doing wrong?
You need to use CSV#rewind
Here is the sample:
require 'csv'
csv = CSV.new(File.new("data1.csv", "r+"), headers: ['name', 'age'], write_headers: true)
csv.add_row(['john', '22'])
csv.add_row(['jane', '24'])
p csv.to_a # Empty array
csv.rewind
p csv.to_a # Array with three CSV::Row objects (including header)
I am trying to convert a CSV file to JSON using Ruby. I am very, very, green when it comes to working with Ruby (or any language for that matter) so the answers may need to be dumbed down for me. Putting it in JSON seems like the most reasonable solution to me because I understand how to work with JSON when assigning variables equal to the attributes that come in the response. If there is a better way to do it, feel free to teach me.
My CSV is in the following format:
Header1,Header,Header3
ValueX,ValueY,ValueZ
I would like to be able to use the data to say something along the lines of this:
For each ValueX in Row 1 after the headers, check if valueZ is > ValueY. If yes, do this, if no do that. I understand how to do the if statement, just now how to parse out my information into variables/arrays.
Any ideas here?
require 'csv'
require 'json'
rows = []
CSV.foreach('a.csv', headers: true, converters: :all) do |row|
rows << row.to_hash
end
puts rows.to_json
# => [{"Header1":"ValueX","Header":"ValueY","Header3":"ValueZ"}]
Here is a first pointer:
require 'csv'
data = CSV.read('your_file.csv', { :col_sep => ',' }
Now you should have the data in data; you can test in irb.
I don't entirely understand the question:
if z > y
# do this
else
# do that
end
For JSON, you should be able to do JSON.parse().
I am not sure what target format JSON requires, probably a Hash.
You can populate your hash with the dataset from the CVS:
hash = Hash.new
hash[key_goes_here] = value_here
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!
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.
I would like to parse a CSV file so that each row is treated like an object with the header-row being the names of the attributes in the object. I could write this, but I'm sure its already out there.
Here is my CSV input:
"foo","bar","baz"
1,2,3
"blah",7,"blam"
4,5,6
The code would look something like this:
CSV.open('my_file.csv','r') do |csv_obj|
puts csv_obj.foo #prints 1 the 1st time, "blah" 2nd time, etc
puts csv.bar #prints 2 the first time, 7 the 2nd time, etc
end
With Ruby's CSV module I believe I can only access the fields by index. I think the above code would be a bit more readable. Any ideas?
Using Ruby 1.9 and above, you can get a an indexable object:
CSV.foreach('my_file.csv', :headers => true) do |row|
puts row['foo'] # prints 1 the 1st time, "blah" 2nd time, etc
puts row['bar'] # prints 2 the first time, 7 the 2nd time, etc
end
It's not dot syntax but it is much nicer to work with than numeric indexes.
As an aside, for Ruby 1.8.x FasterCSV is what you need to use the above syntax.
Here is an example of the symbolic syntax using Ruby 1.9. In the examples below, the code reads a CSV file named data.csv from Rails db directory.
:headers => true treats the first row as a header instead of a data row. :header_converters => :symbolize parameter then converts each cell in the header row into Ruby symbol.
CSV.foreach("#{Rails.root}/db/data.csv", {:headers => true, :header_converters => :symbol}) do |row|
puts "#{row[:foo]},#{row[:bar]},#{row[:baz]}"
end
In Ruby 1.8:
require 'fastercsv'
CSV.foreach("#{Rails.root}/db/data.csv", {:headers => true, :header_converters => :symbol}) do |row|
puts "#{row[:foo]},#{row[:bar]},#{row[:baz]}"
end
Based on the CSV provided by the Poul (the StackOverflow asker), the output from the example code above will be:
1,2,3
blah,7,blam
4,5,6
Depending on the characters used in the headers of the CSV file, it may be necessary to output the headers in order to see how CSV (FasterCSV) converted the string headers to symbols. You can output the array of headers from within the CSV.foreach.
row.headers
Easy to get a hash in Ruby 2.3:
CSV.foreach('my_file.csv', headers: true, header_converters: :symbol) do |row|
puts row.to_h[:foo]
puts row.to_h[:bar]
end
Although I am pretty late to the discussion, a few months ago I started a "CSV to object mapper" at https://github.com/vicentereig/virgola.
Given your CSV contents, mapping them to an array of FooBar objects is pretty straightforward:
"foo","bar","baz"
1,2,3
"blah",7,"blam"
4,5,6
require 'virgola'
class FooBar
include Virgola
attribute :foo
attribute :bar
attribute :baz
end
csv = <<CSV
"foo","bar","baz"
1,2,3
"blah",7,"blam"
4,5,6
CSV
foo_bars = FooBar.parse(csv).all
foo_bars.each { |foo_bar| puts foo_bar.foo, foo_bar.bar, foo_bar.baz }
Since I hit this question with some frequency:
array_of_hashmaps = CSV.read("path/to/file.csv", headers: true)
puts array_of_hashmaps.first["foo"] # 1
This is the non-block version, when you want to slurp the whole file.