Output array to CSV in Ruby

Question

It's easy enough to read a CSV file into an array with Ruby but I can't find any good documentation on how to write an array into a CSV file. Can anyone tell me how to do this?

I'm using Ruby 1.9.2 if that matters.

Answer 1

To a file:

require 'csv'
CSV.open("myfile.csv", "w") do |csv|
  csv << ["row", "of", "CSV", "data"]
  csv << ["another", "row"]
  # ...
end

To a string:

require 'csv'
csv_string = CSV.generate do |csv|
  csv << ["row", "of", "CSV", "data"]
  csv << ["another", "row"]
  # ...
end

Here's the current documentation on CSV: (until 3.1.1 just replace 1.9.2)

https://ruby-doc.org/stdlib-1.9.2/libdoc/csv/rdoc/CSV.html#class-CSV-label-Writing

while 3.1.2 up to latest (3.2.2 as of this edit).

https://ruby-doc.org/3.2.2/stdlibs/csv/CSV.html

Answer 2

If you have an array of arrays of data:

rows = [["a1", "a2", "a3"],["b1", "b2", "b3", "b4"], ["c1", "c2", "c3"]]

Then you can write this to a file with the following, which I think is much simpler:

require "csv"
File.write("ss.csv", rows.map(&:to_csv).join)

Answer 3

I've got this down to just one line.

rows = [['a1', 'a2', 'a3'],['b1', 'b2', 'b3', 'b4'], ['c1', 'c2', 'c3'], ... ]
csv_str = rows.inject([]) { |csv, row|  csv << CSV.generate_line(row) }.join("")
#=> "a1,a2,a3\nb1,b2,b3\nc1,c2,c3\n" 

Do all of the above and save to a csv, in one line.

File.open("ss.csv", "w") {|f| f.write(rows.inject([]) { |csv, row|  csv << CSV.generate_line(row) }.join(""))}

NOTE:

To convert an active record database to csv would be something like this I think

CSV.open(fn, 'w') do |csv|
  csv << Model.column_names
  Model.where(query).each do |m|
    csv << m.attributes.values
  end
end

---

Hmm @tamouse, that gist is somewhat confusing to me without reading the csv source, but generically, assuming each hash in your array has the same number of k/v pairs & that the keys are always the same, in the same order (i.e. if your data is structured), this should do the deed:

rowid = 0
CSV.open(fn, 'w') do |csv|
  hsh_ary.each do |hsh|
    rowid += 1
    if rowid == 1
      csv << hsh.keys# adding header row (column labels)
    else
      csv << hsh.values
    end# of if/else inside hsh
  end# of hsh's (rows)
end# of csv open

If your data isn't structured this obviously won't work

Answer 4

If anyone is interested, here are some one-liners (and a note on loss of type information in CSV):

require 'csv'

rows = [[1,2,3],[4,5]]                    # [[1, 2, 3], [4, 5]]

# To CSV string
csv = rows.map(&:to_csv).join             # "1,2,3\n4,5\n"

# ... and back, as String[][]
rows2 = csv.split("\n").map(&:parse_csv)  # [["1", "2", "3"], ["4", "5"]]

# File I/O:
filename = '/tmp/vsc.csv'

# Save to file -- answer to your question
IO.write(filename, rows.map(&:to_csv).join)

# Read from file
# rows3 = IO.read(filename).split("\n").map(&:parse_csv)
rows3 = CSV.read(filename)

rows3 == rows2   # true
rows3 == rows    # false

Note: CSV loses all type information, you can use JSON to preserve basic type information, or go to verbose (but more easily human-editable) YAML to preserve all type information -- for example, if you need date type, which would become strings in CSV & JSON.

Answer 5

Building on @boulder_ruby's answer, this is what I'm looking for, assuming us_eco contains the CSV table as from my gist.

CSV.open('outfile.txt','wb', col_sep: "\t") do |csvfile|
  csvfile << us_eco.first.keys
  us_eco.each do |row|
    csvfile << row.values
  end
end

Updated the gist at https://gist.github.com/tamouse/4647196

Answer 6

Struggling with this myself. This is my take:

https://gist.github.com/2639448:

require 'csv'

class CSV
  def CSV.unparse array
    CSV.generate do |csv|
      array.each { |i| csv << i }
    end
  end
end

CSV.unparse [ %w(your array), %w(goes here) ]