Match pattern in Ruby with Regexp - ruby

Question

Lets say we have the following array of strings (this array is a lot bigger):
[
'http://www.example.com?id=123456',
'http://www.example.com?id=234567'
]
As you can see, everything up to the first digit is the same in both strings. Is there a way to easily find what both strings have in common and what is different? So that I get a string like 'http://www.example.com?id=' and and array like ['123456', '234567'].

Answer 1

Here's a method to find the longest common prefix in an array.
def _lcp(str1, str2)
end_index = [str1.length, str2.length].min - 1
end_index.downto(0) do |i|
return str1[0..i] if str1[0..i] == str2[0..i]
end
''
end
def lcp(strings)
strings.inject do |acc, str|
_lcp(acc, str)
end
end
lcp [
'http://www.example.com?id=123456',
'http://www.example.com?id=234567',
'http://www.example.com?id=987654'
]
#=> "http://www.example.com?id="
lcp [
'http://www.example.com?id=123456',
'http://www.example.com?id=123457'
]
#=> "http://www.example.com?id=12345"

Answer 2

# This is an approach using higher level ruby std-lib components instead of a regex.
# Why re-invent the wheel?
module UriHelper
require 'uri'
require 'cgi'
# Take an array of urls and extract the id parameter.
# #param urls {Array} an array of urls to parse
# #returns {Array}
def UriHelper.get_id_params( urls )
urls.map do |u|
puts u
uri = URI(u)
params = CGI::parse(uri.query)
params["id"].first # returned
end
end
end
require "test/unit"
# This is unit test proving our helper works as intended
class TestUriHelper < Test::Unit::TestCase
def test_get_id_params
urls = [
'http://www.example.com?id=123456',
'http://www.example.com?id=234567'
]
assert_equal("123456", UriHelper.get_id_params(urls).first )
assert_equal("234567", UriHelper.get_id_params(urls).last )
end
end