From: Ryan Davis <ryand-ruby@...>
Date: 2011-02-22T06:15:21+09:00
Subject: Re: Regular expressions, strange result from .scan method


On Feb 21, 2011, at 13:10 , John Doe wrote:

> I'm having some strange result from the .scan method used on a string.
> 
> Here's my code :
> 
> a = "counter-46382764"
> r = /counter-(\d+)/
> 
> puts (a.scan(r)).inspect
> 
> It prints : [ [ "46382764" ] ]
> 
> I was expecting : [ "46382764" ]
> (just a simple array not an array in an array)
> 
> What's wrong with me ? :/

Besides not reading the documentation, probably nothing. :P

% irb
>> "counter-46382764".scan(/counter-(\d+)/)
=> [["46382764"]]
>> "counter-46382764".scan(/counter-\d+/)
=> ["counter-46382764"]
>> "counter-46382764".scan(/\d+/)
=> ["46382764"]
>> ri "String.scan"
= String.scan

(from ruby core)
------------------------------------------------------------------------------
  str.scan(pattern)                         => array
  str.scan(pattern) {|match, ...| block }   => str

------------------------------------------------------------------------------

Both forms iterate through str, matching the pattern (which may be a
Regexp or a String). For each match, a result is generated and either added to
the result array or passed to the block. If the pattern contains no groups,
each individual result consists of the matched string, $&.  If the pattern
contains groups, each individual result is itself an array containing one
entry per group.
     
       a = "cruel world"
       a.scan(/\w+/)        #=> ["cruel", "world"]
       a.scan(/.../)        #=> ["cru", "el ", "wor"]
       a.scan(/(...)/)      #=> [["cru"], ["el "], ["wor"]]
       a.scan(/(..)(..)/)   #=> [["cr", "ue"], ["l ", "wo"]]
     

And the block form:
     
       a.scan(/\w+/) {|w| print "<<#{w}>> " }
       print "\n"
       a.scan(/(.)(.)/) {|x,y| print y, x }
       print "\n"
     

produces:
     
       <<cruel>> <<world>>
       rceu lowlr