Ruby - reading from .csv and creating objects out of it

Question

I have .csv file with rows of which every row represents one call with certain duration, number etc. I need to create array of Call objects - every Call.new expects Hash of parameters, so it's easy - it just takes rows from CSV. But for some reason it doesn't work - when I invoke Call.new(raw_call) it's nil. It's also impossible for me to see any output - I placed puts in various places in code (inside blocks etc) and it simply doesn't show anything. I obviously have another class - Call, which holds initialize for Call etc.

require 'csv'
class CSVCallParser
  attr_accessor :io

  def initialize(io)
    self.io = io
  end

  NAMES = {
    a: :date,
    b: :service,
    c: :phone_number,
    d: :duration,
    e: :unit,
    f: :cost
  }

  def run
    parse do |raw_call| 
    parse_call(raw_call)
    end
  end

  private

  def parse_call(raw_call) 
    NAMES.each_with_object({}) do |name, title, memo|
      memo[name] = raw_call[title.to_s]
    end
  end

  def parse(&block) 
    CSV.parse(io, headers: true, header_converters: :symbol, &block)
  end

end

CSVCallParser.new(ARGV[0]).run

Small sample of my .csv file: headers and one row:

"a","b","c","d","e","f"
"01.09.2016 08:49","International","48627843111","0:29","","0,00"

can you provide a small sample of the csv file you are working with? So I can try to reproduce your code and see what's happening — davidhu
– davidhu, Commented Oct 5, 2016 at 15:23

davidhu · Accepted Answer · 2016-10-05 16:41:03Z

2

I noticed a few things that isn't going as expected. In the parse_call method,

def parse_call(raw_call) 
  NAMES.each_with_object({}) do |name, title, memo|
    memo[name] = raw_call[title.to_s]
  end
end

I tried to print name, title, and memo. I expected to get :a, :date, and {}, but what I actually got was [:a,:date],{}, and nil.

Also, raw_call headers are :a,:b,:c..., not :date, :service..., so you should be using raw_call[name], and converting that to string will not help, since the key is a symbol in the raw_call.

So I modified the function to

def parse_call(raw_call) 
  NAMES.each_with_object({}) do |name_title, memo|
    memo[name_title[1]] = raw_call[name_title[0]]
  end
end

name_title[1] returns the title (:date, :service, etc)

name_title[0] returns the name (:a, :b, etc)

Also, in this method

def run
  parse do |raw_call| 
    parse_call(raw_call)
  end
end

You are not returning any results you get, so you are getting nil,

So, I changed it to

  def run
    res = []
    parse do |raw_call| 
      res << parse_call(raw_call)
    end
    res 
  end

Now, if I output the line

p CSVCallParser.new(File.read("file1.csv")).run

I get (I added two more lines to the csv sample)

[{:date=>"01.09.2016 08:49", :service=>"International", :phone_number=>"48627843111", :duration=>"0:29", :unit=>"", :cost=>"0,00"},
 {:date=>"02.09.2016 08:49", :service=>"International", :phone_number=>"48622454111", :duration=>"1:29", :unit=>"", :cost=>"0,00"}, 
 {:date=>"03.09.2016 08:49", :service=>"Domestic", :phone_number=>"48627843111", :duration=>"0:29", :unit=>"", :cost=>"0,00"}]

If you want to run this program from the terminal like so

ruby csv_call_parser.rb calls.csv

(In this case, calls.csv is passed in as an argument to ARGV)

You can do so by modifying the last line of the ruby file.

p CSVCallParser.new(File.read(ARGV[0])).run

This will also return the array with hashes like before.

edited Oct 5, 2016 at 16:41

answered Oct 5, 2016 at 15:52

davidhu

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3 Comments

Jes Over a year ago

Thank you very very much, your modifications are getting me closer to full understanding of a problem. There's one more thing, I wanted to run program like this: ruby csv_call_parser.rb calls.csv, so I can get my results like this: CSVCallParser.new(ARGV[0]).run or CSVCallParser.new(File.read(ARGV[0]).run, but none of this work

davidhu Over a year ago

See my update. What I did seems to be similar to what you have in your comment, but I was able to print out the hash array to the terminal.

Jes Over a year ago

Thank you very much, you have no idea how you helped me! So the main problem was using name and title? Using them as name_title[0] and [1] made all the difference?

Daniel Garmoshka · Accepted Answer · 2022-05-26 04:19:10Z

0

csv = CSV.parse(csv_text, :headers => true)
puts csv.map(&:to_h)

outputs:

[{a:1, b:1}, {a:2, b:2}]

answered May 26, 2022 at 4:19

Daniel Garmoshka

6,39847 silver badges47 bronze badges

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