Output array to CSV in Ruby

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.

6 Answers

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)

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

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) 

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

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.

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

Struggling with this myself. This is my take:

:

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) ]