Ruby: How to add two lines at once to a csv?

Question

I have a list of items and a script which generates two lines of csv for each item. May I add two lines at once to csv generator? I want something like this:

CSV.generate do |csv|
  items.each do |item|
    csv << rows(item)
  end
end

def rows(item)
  return \
    ['value1', 'value2', 'value2'],
    ['value3', 'value4', 'value5']
end

But csv << can't receive two lines at once.

Now my the best code is:

CSV.generate do |csv|
  items.each do |item|
    rows(item).each { |row| csv << row } 
  end
end

Update: Now the best code without adding two line at once looks like:

CSV.generate do |csv|
  items.
    flat_map(&method(:rows)).
    each(&csv.method(:<<))
end

Aleksei Matiushkin · Accepted Answer · 2017-05-24 07:35:22Z

1

CSV.generate do |csv|
  csv << items.flat_map(&method(:rows))
end

answered May 24, 2017 at 7:35

Aleksei Matiushkin

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3 Comments

TeWu Over a year ago

This doesn't generate clean CSV string, but rather something like that: "[""value1"", ""value2"",... (tested on Ruby 2.2.4)

Ilya Lavrov Over a year ago

I like an idea with &method(:rows) but the code gives wrong result.

TeWu Over a year ago

@IlyaLavrov You can make it work by doing items.flat_map(&method(:rows)).each(&csv.method(:<<)), but your version (from the question) is IMO soo much more cleaner.

steenuil · Accepted Answer · 2017-05-24 08:41:18Z

1

Array#push or Array#append work the same way, and can take multiple arguments. Edit: As it turns out, CSV.generate yields a CSV object which has neither of those methods.

You can also do it like this:

CSV.generate do |csv|
  items.each do |item|
    r = rows(item)
    csv << r[0] << r[1]
  end
end

edited May 24, 2017 at 8:41

answered May 24, 2017 at 8:05

steenuil

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2 Comments

TeWu Over a year ago

CSV object doesn't have append method

steenuil Over a year ago

@TeWu Thanks, I didn't notice.

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