Export Ruby Hash to CSV [duplicate] - ruby-on-rails

Question

I am new in ruby so please forgive the noobishness.
I have a CSV with two columns. One for animal name and one for animal type.
I have a hash with all the keys being animal names and the values being animal type. I would like to write the hash to the CSV without using fasterCSV. I have thought of several ideas what would be easiest.. here is the basic layout.
require "csv"
def write_file
h = { 'dog' => 'canine', 'cat' => 'feline', 'donkey' => 'asinine' }
CSV.open("data.csv", "wb") do |csv|
csv << [???????????]
end
end
When I opened the file to read from it I opened it File.open("blabla.csv", headers: true)
Would it be possible to write back to the file the same way?

Answer 1

If you want column headers and you have multiple hashes:
require 'csv'
hashes = [{'a' => 'aaaa', 'b' => 'bbbb'}]
column_names = hashes.first.keys
s=CSV.generate do |csv|
csv << column_names
hashes.each do |x|
csv << x.values
end
end
File.write('the_file.csv', s)
(tested on Ruby 1.9.3-p429)

Answer 2

Try this:
require 'csv'
h = { 'dog' => 'canine', 'cat' => 'feline', 'donkey' => 'asinine' }
CSV.open("data.csv", "wb") {|csv| h.to_a.each {|elem| csv << elem} }
Will result:
1.9.2-p290:~$ cat data.csv
dog,canine
cat,feline
donkey,asinine

Answer 3

I think the simplest solution to your original question:
def write_file
h = { 'dog' => 'canine', 'cat' => 'feline', 'donkey' => 'asinine' }
CSV.open("data.csv", "w", headers: h.keys) do |csv|
csv << h.values
end
end
With multiple hashes that all share the same keys:
def write_file
hashes = [ { 'dog' => 'canine', 'cat' => 'feline', 'donkey' => 'asinine' },
{ 'dog' => 'rover', 'cat' => 'kitty', 'donkey' => 'ass' } ]
CSV.open("data.csv", "w", headers: hashes.first.keys) do |csv|
hashes.each do |h|
csv << h.values
end
end
end

Answer 4

CSV can take a hash in any order, exclude elements, and omit a params not in the HEADERS
require "csv"
HEADERS = [
'dog',
'cat',
'donkey'
]
def write_file
CSV.open("data.csv", "wb", :headers => HEADERS, :write_headers => true) do |csv|
csv << { 'dog' => 'canine', 'cat' => 'feline', 'donkey' => 'asinine' }
csv << { 'dog' => 'canine'}
csv << { 'cat' => 'feline', 'dog' => 'canine', 'donkey' => 'asinine' }
csv << { 'dog' => 'canine', 'cat' => 'feline', 'donkey' => 'asinine', 'header not provided in the options to #open' => 'not included in output' }
end
end
write_file # =>
# dog,cat,donkey
# canine,feline,asinine
# canine,,
# canine,feline,asinine
# canine,feline,asinine
This makes working with the CSV class more flexible and readable.

Answer 5

I tried the solutions here but got an incorrect result (values in wrong columns) since my source is a LDIF file that not always has all the values for a key. I ended up using the following.
First, when building up the hash I remember the keys in a separate array which I extend with the keys that are not allready there.
# building up the array of hashes
File.read(ARGV[0]).each_line do |lijn|
case
when lijn[0..2] == "dn:" # new record
record = {}
when lijn.chomp == '' # end record
if record['telephonenumber'] # valid record ?
hashes << record
keys = keys.concat(record.keys).uniq
end
when ...
end
end
The important line here is keys = keys.concat(record.keys).uniq which extends the array of keys when new keys (headers) are found.
Now the most important: converting our hashes to a CSV
CSV.open("export.csv", "w", {headers: keys, col_sep: ";"}) do |row|
row << keys # add the headers
hashes.each do |hash|
row << hash # the whole hash, not just the array of values
end
end

Answer 6

[BEWARE] All the answers in this thread are assuming that the order of the keys defined in the hash will be constant amongst all rows.
To prevent problems (that I am facing right now) where some values are assigned to the wrong keys in the csv (Ex:)
hahes = [
{:cola => "hello", :colb => "bye"},
{:colb => "bye", :cola => "hello"}
]
producing the following table using the code from the majority (including best answer) of the answers on this thread:
cola | colb
-------------
hello | bye
-------------
bye | hello
You should do this instead:
require "csv"
csv_rows = [
{:cola => "hello", :colb => "bye"},
{:colb => "bye", :cola => "hello"}
]
column_names = csv_rows.first.keys
s=CSV.generate do |csv|
csv << column_names
csv_rows.each do |row|
csv << column_names.map{|column_name| row[column_name]} #To be explicit
end
end

Answer 7

Try this:
require 'csv'
data = { 'one' => '1', 'two' => '2', 'three' => '3' }
CSV.open("data.csv", "a+") do |csv|
csv << data.keys
csv << data.values
end

Answer 8

Lets we have a hash,
hash_1 = {1=>{:rev=>400, :d_odr=>3}, 2=>{:rev=>4003, :d_price=>300}}
The above hash_1 having keys as some id 1,2,.. and values to those are again hash with some keys as (:rev, :d_odr, :d_price).
Suppose we want a CSV file with headers,
headers = ['Designer_id','Revenue','Discount_price','Impression','Designer ODR']
Then make a new array for each value of hash_1 and insert it in CSV file,
CSV.open("design_performance_data_temp.csv", "w") do |csv|
csv << headers
csv_data = []
result.each do |design_data|
csv_data << design_data.first
csv_data << design_data.second[:rev] || 0
csv_data << design_data.second[:d_price] || 0
csv_data << design_data.second[:imp] || 0
csv_data << design_data.second[:d_odr] || 0
csv << csv_data
csv_data = []
end
end
Now you are having design_performance_data_temp.csv file saved in your corresponding directory.
Above code can further be optimized.