Let's say I had the string
"[1,2,[3,4,[5,6]],7]"
How would I parse that into the array
[1,2,[3,4,[5,6]],7]
?
Nesting structures and patterns are completely arbitrary in my usage case.
My current ad-hoc solution involves adding a space after every period and using YAML.load, but I'd like to have a cleaner one if possible.
(One that does not require external libraries if possible)
That particular example is being parsed correctly using JSON:
s = "[1,2,[3,4,[5,6]],7]"
#=> "[1,2,[3,4,[5,6]],7]"
require 'json'
#=> true
JSON.parse s
#=> [1, 2, [3, 4, [5, 6]], 7]
If that doesn't work, you can try running the string through eval, but you have to ensure that no actual ruby code has been passed, as eval could be used as injection vulnerability.
Edit: Here is a simple recursive, regex based parser, no validation, not tested, not for production use etc:
def my_scan s
res = []
s.scan(/((\d+)|(\[(.+)\]))/) do |match|
if match[1]
res << match[1].to_i
elsif match[3]
res << my_scan(match[3])
end
end
res
end
s = "[1,2,[3,4,[5,6]],7]"
p my_scan(s).first #=> [1, 2, [3, 4, [5, 6]], 7]
JSON.parse IMHO.JSON is part of Ruby core lib, at least in 1.9.x.
s = "['hello', 2, 'test', 5.0]", JSON will fail to parse with a generic error unexpected token at .... However, YAML does work as shown in @Arup's answer: YAML.load(s) => ["hello", 2, "test", 5.0].The same can be done using Ruby standard libaray YAML as below :
require 'yaml'
s = "[1,2,[3,4,[5,6]],7]"
YAML.load(s)
# => [1, 2, [3, 4, [5, 6]], 7]
"['hello', 2, 'test', 5.0]", where JSON fails to parse.
"Obviously" the best solution is to write your own parser. [ If you like writing parsers, have never done it before and want to learn something new, or want control over the exact grammar ]
require 'parslet'
class Parser < Parslet::Parser
rule(:space) { str(' ') }
rule(:space?) { space.repeat(0) }
rule(:openbrace_) { str('[').as(:op) >> space? }
rule(:closebrace_) { str(']').as(:cl) >> space? }
rule(:comma_) { str(',') >> space? }
rule(:integer) { match['0-9'].repeat(1).as(:int) }
rule(:value) { (array | integer) >> space? }
rule(:list) { value >> ( comma_ >> value ).repeat(0) }
rule(:array) { (openbrace_ >> list.maybe.as(:list) >> closebrace_ )}
rule(:nest) { space? >> array.maybe }
root(:nest)
end
class Arr
def initialize(args)
@val = args
end
def val
@val.map{|v| v.is_a?(Arr) ? v.val : v}
end
end
class MyTransform < Parslet::Transform
rule(:int => simple(:x)) { Integer(x) }
rule(:op => '[', :cl => ']') { Arr.new([]) }
rule(:op => '[', :list => simple(:x), :cl => ']') { Arr.new([x]) }
rule(:op => '[', :list => sequence(:x), :cl => ']') { Arr.new(x) }
end
def parse(s)
MyTransform.new.apply(Parser.new.parse(s)).val
end
parse " [ 1 , 2 , [ 3 , 4 , [ 5 , 6 , [ ]] ] , 7 ] "
Parslet transforms will match a single value as "simple" but if that value returns an array, you soon get arrays of arrays, then you have to start using subtree. returning objects however are fine as they represent a single value when transforming the layer above... so sequence will match fine.
Couple the trouble with returning bare arrays, with the problem that Array([x]) and Array(x) give you the same thing... and you get very confusing results.
To avoid this I made a helper class called Arr which represents an array of items. I could then dictate what I pass into it. Then I can get the parser to keep all the brackets even if you have the example that @MateuszFryc called out :) (thanks @MateuszFryc)
rule(:op => '[', :cl => ']') { Arr.new([]) } is never matched? as you thought it would be. This is rather matched by rule(:op => '[', :list => simple(:x), :cl => ']') { Arr.new([x]) }, thus the problem.rule(:op => '[', :list => simple(:x), :cl => ']') { Arr.new([x].compact) } and one which you think is used rule(:op => '[', :cl => ']') { Arr.new([]) }, delete completely.Use eval
array = eval("[1,2,[3,4,[5,6]],7]")
