I have an array of objects, where the objects are instances of a class. I would like to save this array into a file in such format that I could read the file back to an array and the objects and its' instance variable values would be as they were before saving. Does someone know how this could be achieved?
The class instance objects that I would like to save to a file are fairly complex containing tens of instance variables that are often other class instance variables themselves.
WHAT I HAVE TRIED:
According to this post I tried the following:
TRIAL1:
Save file:
require 'pp'
$stdout = File.open('path/to/file.txt', 'w')
pp myArray
Load file:
require 'rubygems'
require 'json'
buffer = File.open('path/to/file.txt', 'r').read
myArray = JSON.parse(buffer)
but I got a JSON::ParserError
TRIAL2:
Save file
serialized_array = Marshal.dump(myArray)
File.open('./myArray.txt', 'w') {|f| f.write(serialized_array) }
received Encoding::UndefinedConversionError
TRIAL1 doesn't work because pp "prints arguments in pretty form" and that's not necessarily JSON.
TRIAL2 probably isn't working because Marshal produces binary data (not text) and you're not working with your file in binary mode, that could lead to encoding and EOL problems. Besides, Marshal isn't a great format for persistence since the format is tied to the version of Ruby you're using.
A modification of TRIAL1 to write JSON is probably the best solution these days:
require 'json'
File.open('path/to/file.json', 'w') { |f| JSON.dump(myArray, f) }
Finally managed to find a solution that worked!
dump = Marshal.dump(myArray)
File.write('./myarray', myArray, mode: 'r+b')
dump = File.read('./myarray')
user = Marshal.restore(dump)
Marshall was able to do the trick after changing the encoding to binary mode
Given a link to download a CSV(clicking on the link downloads the CSV instead of opening it in a browser), can I read it using CSV.read()? I know that I can do it using:
CSV.new(open(params[:ad_csv]), headers: true).each |row|
puts row # ad dict with header value as keys
end
I can't read the csv like this CSV.read(open(params[:ad_csv]), headers: true, read_timeout: 600)
I read the documentation but it didn't clear things up for me. Hence my question, difference between CSV.read() and CSV.new().
CSV.new just initializes an instance of CSV that can be assigned to a variable and can be used to read from or write to.
Whereas CSV.read initializes an instance of CSV and immediately reads its content into an array. From the docs:
Use read to slurp a CSV file into an Array of Arrays. Pass the path to the file and any options ::new understands.
Simplified (very simplified) CSV.read is implemented like this:
def self.read(path, *options)
new(path, *options) { |csv| csv.read }
end
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 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.)
I have a csv file, some hockey stats, for example:
09.09.2008,1,HC Vitkovice Steel,BK Mlada Boleslav,1:0 (PP)
09.09.2008,1,HC Lasselsberger Plzen,RI OKNA ZLIN,6:2
09.09.2008,1,HC Litvinov,HC Sparta Praha,3:5
I want to save them in an array of hashes. I don't have any headers and I would like to add keys to each value like "time" => "09.09.2008" and so on. Each line should by accessible like arr[i], each value by for example arr[i]["time"]. I prefer CSV class rather than FasterCSV or split. Can you show the way or redirect to some thread where a similar problem was solved?
Just pass headers: true
CSV.foreach(data_file, headers: true) do |row|
puts row.inspect # hash
end
From there, you can manipulate the hash however you like.
(Tested with Ruby 2.0, but I think this has worked for quite a while.)
Edit
You say you don't have any headers - could you add a header line to the beginning of the file contents after reading them?
You can use the Ruby CSV parser to parse it, and then use Hash[ keys.zip(values) ] to make it a hash.
Example:
test = '''
09.09.2008,1,HC Vitkovice Steel,BK Mlada Boleslav,1:0 (PP)
09.09.2008,1,HC Lasselsberger Plzen,RI OKNA ZLIN,6:2
09.09.2008,1,HC Litvinov,HC Sparta Praha,3:5
'''.strip
keys = ['time', etc... ]
CSV.parse(test).map {|a| Hash[ keys.zip(a) ] }
This is a fantastic post by Josh Nichols which explains how to do what you're asking.
To summarize, here his code:
csv = CSV.new(body, :headers => true, :header_converters => :symbol, :converters => [:all, :blank_to_nil])
csv.to_a.map {|row| row.to_hash }
=> [{:year=>1997, :make=>"Ford", :model=>"E350", :description=>"ac, abs, moon", :price=>3000.0}, {:year=>1999, :make=>"Chevy", :model=>"Venture \"Extended Edition\"", :description=>nil, :price=>4900.0}, {:year=>1999, :make=>"Chevy", :model=>"Venture \"Extended Edition, Very Large\"", :description=>nil, :price=>5000.0}, {:year=>1996, :make=>"Jeep", :model=>"Grand Cherokee", :description=>"MUST SELL!\nair, moon roof, loaded", :price=>4799.0}]
So, you could save the body of your CSV file into a string called body.
body = "09.09.2008,1,HC Vitkovice Steel,BK Mlada Boleslav,1:0 (PP)
09.09.2008,1,HC Lasselsberger Plzen,RI OKNA ZLIN,6:2
09.09.2008,1,HC Litvinov,HC Sparta Praha,3:5"
And then run his code as listed above on it.
A little shorter solution
Parse string:
CSV.parse(content, headers: :first_row).map(&:to_h)
Parse file:
CSV.open(filename, headers: :first_row).map(&:to_h)
Slight variation on Nathan Long's answer
data_file = './sheet.csv'
data = CSV.foreach(data_file, headers: true).map(&:to_h)
Now data is an array of hashes to do your bidding with!
The headers option to the CSV module accepts an array of strings to be used as the headers, when they're not present as the first row in the CSV content.
CSV.parse(content, headers: %w(time number team_1 team_2 score))
This will generate an enumerable of hashes using the given headers as keys.
You can try the following gem also
require 'csv_hasher'
arr_of_hashes = CSVHasher.hashify('/path/to/csv/file')
The keys of the returned hashes will be the header values of the csv file.
If you want to pass your own keys then
keys = [:key1, :key2, ... ]
arr_of_hashers = CSVHasher.hashify('/path/to/csv/file', { keys: keys })
I guess this is the shortest version:
keys = ["time", ...]
CSV.parse(content, headers: keys).map(&:to_h)
you could also use the SmarterCSV gem,
which returns data from CSV files as Ruby hashes by default.
It has a lot of features, including processing the data in chunks, which is very benefitial for huge data files.
require 'smarter_csv'
options = {} # see GitHub README
data = SmarterCSV.process(your_file_name, options)