How to parse output of array.inspect back into an array

Question

I want to store multidimensional arrays in text files and reload them efficiently. The tricky part is that the array includes strings which could look like " ] , [ \\\"" or anything.

Easiest way of writing the table to file is just as my_array.inspect (right?)

How do I then recreate the array as quickly and painlessly as possible from a string read back from the text file that might look like "[\" ] , [ \\\\\\\"\"]" (as in the above case)?

It might help if you could post an example of your text file so we can see exactly what you're trying to accomplish. — Caley Woods
– Caley Woods, Commented Jun 23, 2011 at 13:59

sawa · Accepted Answer · 2011-06-23 18:23:07Z

4

If your array only includes objects that are literally written such as Numerals, Strings, Arrays, Hashes, you can use eval.

a = [1, 2, 3].inspect
# => "[1, 2, 3]"

eval(a)
# => [1, 2, 3]

edited Jun 23, 2011 at 18:23

answered Jun 23, 2011 at 14:17

sawa

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3 Comments

Nat Over a year ago

That's exactly what I wanted to know. Although I went with the YAML option anyway.

Kudu Over a year ago

eval() is evil and it's slow. Just saying.

Seamus Abshere Over a year ago

I agree with Kudu, eval() is the wrong approach. Use plaintext (Yaml, JSON) or binary (Marshal) but be very careful relying on executing arbitrary Ruby code as a form of serialization.

Kudu · Accepted Answer · 2011-06-23 14:14:06Z

2

In my opinion, this sounds like too much trouble. Use YAML instead.

require 'yaml'
a = [ [ [], [] ], [ [], [] ] ]
File.open("output.yml", "w") do |f|
  f.write a.to_yaml
end
b = YAML.load File.open('output.yml', 'r')

As an alternative, you could use JSON instead.

edited Jun 23, 2011 at 14:14

answered Jun 23, 2011 at 14:06

Kudu

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Comments

Seamus Abshere · Accepted Answer · 2011-06-23 14:01:02Z

0

Say you have array

ary

You could write the array to a file:

File.open(path, 'w') { |f| f.write Marshal.dump(ary) }

and then re-create the array by reading the file into a string and saying

ary = Marshal.load(File.read(path))

answered Jun 23, 2011 at 14:01

Seamus Abshere

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3 Comments

Kudu Over a year ago

Interesting solution, but binary serialization has it's own set of issues. I try to avoid Marshal / pickle in production, resorting instead to YAML or JSON.

Seamus Abshere Over a year ago

If you want a plaintext serialization format, you might want to use the yajl-ruby gem... they say it's even faster than Marshal... replace "Marshal.dump" with "Yajl::Encoder.encode" and "Marshal.load" with "Yajl::Parser.parse"

Kudu Over a year ago

Nat, binary serialization is tricky and works for one programming language only. With YAML or JSON, you can load the array into Ruby, Python, C, etc. Also, if something doesn't work the way it should, you can look at the text file to debug it, instead of parsing the binary data.

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