How can I save an object to a file?

Question

I would like to save an object to a file, and then read it from the file easily. As a simple example, lets say I have the following 3d array:

m = [[[0, 0, 0]         


        

Answer 1

See Marshal: http://ruby-doc.org/core/classes/Marshal.html

-or-

YAML: http://www.ruby-doc.org/core/classes/YAML.html

Answer 2

YAML and Marshal are the most obvious answers, but depending on what you're planning to do with the data, sqlite3 may be a useful option too.

require 'sqlite3'

m = [[[0, 0, 0],
 [0, 0, 0],
 [0, 0, 0]],
[[0, 0, 0],
 [0, 0, 0],
 [0, 0, 0]]]

db=SQLite3::Database.new("demo.out")
db.execute("create table data (x,y,z,value)")
inserter=db.prepare("insert into data (x,y,z,value) values (?,?,?,?)")
m.each_with_index do |twod,z|
  twod.each_with_index do |row,y|
    row.each_with_index do |val,x|
      inserter.execute(x,y,z,val)
    end
  end
end

Answer 3

You need to serialize the objects before you could save them to a file and deserialize them to retrieve them back. As mentioned by Cory, 2 standard serialization libraries are widely used, Marshal and YAML.

Both Marshal and YAML use the methods dump and load for serializing and deserializing respectively.

Here is how you could use them:

m = [
     [
      [0, 0, 0],
      [0, 0, 0],
      [0, 0, 0]
     ],
     [
      [0, 0, 0],
      [0, 0, 0],
      [0, 0, 0]
     ]
    ]

# Quick way of opening the file, writing it and closing it
File.open('/path/to/yaml.dump', 'w') { |f| f.write(YAML.dump(m)) }
File.open('/path/to/marshal.dump', 'wb') { |f| f.write(Marshal.dump(m)) }

# Now to read from file and de-serialize it:
YAML.load(File.read('/path/to/yaml.dump'))
Marshal.load(File.read('/path/to/marshal.dump'))

You need to be careful about the file size and other quirks associated with File reading / writing.

More info, can of course be found in the API documentation.