From: "Peña, Botp" <botp@...>
Date: 2008-06-23T10:32:51+09:00
Subject: Re: Regex - Exclude Multiple Characters and Global Scanning

From: Ben Woodcroft [mailto:donttrustben@gmail.com] 
# David A. Black wrote:
# > irb(main):029:0> offsets = []
# > => []
# > irb(main):030:0> str.scan(/ll./) { offsets << $~.offset(0)[1] }
# > => "llgllallo"
# > irb(main):031:0> offsets
# > => [3, 6, 9]
# That will work, thanks. It would seem intuitive to me that scan (or a 
# method like it) would iterate of MatchData objects, but 

$~ is MatchData
you could wrap dBlack's hint if you want something similar to #scan

eg,

class String
  def mapscan pattern
    atemp=[]
    scan(pattern){ atemp << yield($~)}
    atemp
  end
end
#=> nil

s
#=> "llgllallo"

s.mapscan(/ll./){|md| [md[0],md.offset(0)]}
#=> [["llg", [0, 3]], ["lla", [3, 6]], ["llo", [6, 9]]]

# 
# >> --------------Question 2-----------------------
# >> Now an old gap in my regex understanding. How do I exclude on
# >> consecutive characters? I want something like [^abc], 
# except aba or bbc
# >> is ok, just not 'abc'. Summing this up:
# > 
# > [^abc] means: match one character that is not 'a', not 'b', and not
# > 'c'. I don't think that's what you mean.
# >> reg = /something/
# >> 'abc'.match(reg) #-> no match
# >> 'cba'.match(reg) #-> match
# >> And then I want to be able to do OR operations too, like 
# not 'abc' and
# >> not 'bbc', but that is probably another step of complexity.
# > You can use (?!), which is negative lookahead.
# > irb(main):033:0> reg = /(?!abc)[abc]{3}/
# > => /(?!abc)[abc]{3}/
# > So that means: three of a, b, c, as long as we're not looking at
# > "abc" when we start looking for those three characters.
# > irb(main):034:0> reg.match("abc")
# > => nil
# > irb(main):035:0> reg.match("abb")
# > => #<MatchData:0x69de8>
# > irb(main):036:0> reg.match("cba")
# > => #<MatchData:0x63de4>
# That is exactly what I meant. I was unaware of the negative lookahead 
# operator. Thanks!

if you want to compare sequences, you can create a complete sequence for your case, so you do not end up creating many regex pattern. and then test everything from there.

eg,

SEQALPHA=("a".."z").to_a.join
#=> "abcdefghijklmnopqrstuvwxyz"
SEQALPHA.match "abc"
#=> #<MatchData:0x2906288>
SEQALPHA.match "def"
#=> #<MatchData:0x28ff870>
SEQALPHA.match "xyz"
#=> #<MatchData:0x28fb4a0>
SEQALPHA.match "bac"
#=> nil
SEQALPHA.match "cba"
#=> nil
SEQALPHA.match "yyy"
#=> nil

negating it on your case is simple,

not SEQALPHA.match "bac"
#=> true
not SEQALPHA.match "abc"
#=> false

now using mapscan above, you can do,
SEQALPHA.mapscan(/abc|xyz/){|md| [md[0],md.offset(0)]}
#=> [["abc", [0, 3]], ["xyz", [23, 26]]]


btw, index is a faster if you just want simple string compar.
SEQALPHA.index "abc"
#=> 0
SEQALPHA.index "def"
#=> 3
SEQALPHA.index "xxx"
#=> nil
SEQALPHA.index "bac"
#=> nil
SEQALPHA.index /abc/
#=> 0
SEQALPHA.index /def/
#=> 3
SEQALPHA.index /efd/
#=> nil

again, negating is simple

not SEQALPHA.index /def/
#=> false
not SEQALPHA.index /fde/
#=> true

hth.
kind regards -botp