Hi --

On Fri, 9 May 2008, Todd Benson wrote:

>  On Thu, May 8, 2008 at 7:00 PM, Joel VanderWerf <vjoel@[...].edu> wrote:
> > Todd Benson wrote:
> >>
> >> On Thu, May 8, 2008 at 6:07 PM, ara.t.howard <ara.t.howard@[...].com>
> >> wrote:
> >>>
> >>> On May 8, 2008, at 3:40 PM, Todd Benson wrote:
> >>>>
> >>>> This question arises out of a couple of recent threads and may or may
> >>>> not be a Ruby-specific question.
> >>>>
> >>>> I can check with a character class if one of the characters in the
> >>>> class exists or does not exist, but can I use a regexp to check if a
> >>>> string absolutely contains all of the characters in the class?
> >>>>
> >>>> Using a set perspective, I can do it like this in irb...
> >>>>
> >>>> s1 = "hello there"
> >>>> s2 = "ohi"
> >>>> (s2.unpack('c*') & s1.unpack('c*')).size == s2.size
> >>>>
> >>>> => false
> >>>>
> >>>> I use unpack to avoid creating a bunch of String objects, one for each
> >>>> element in the array, which would happen if I used #split.  What I'm
> >>>> wondering is if there is a way to do this with a simple regexp.
> >>>>
> >>>> Thanks,
> >>>> Todd
> >>>
> >>> cfp:~ > cat a.rb
> >>> class String
> >>>  def all_chars? chars
> >>>   tr(chars, '').empty?
> >>>  end
> >>> end
> >>>
> >>> p 'foobar'.all_chars?('rabof')
> >>> p 'foobar'.all_chars?('abc')
> >>> p 'foobar'.all_chars?('')
> >>>
> >>>
> >>>
> >>> cfp:~ > ruby a.rb
> >>> true
> >>> false
> >>> false
> >>
> >> Cool :)  #tr is one of those useful methods I somehow consistently forget
> >> about.
> >
> > But it can be done with regex, right? It's just more elegant with tr.
> >
> > class String
> >  def all_chars? chars
> >    if chars.empty?
> >      empty?
> >    else
> >      /\A[#{chars}]*\z/ === self
> >    end
> >  end
> > end
> >
> > p 'foobar'.all_chars?('rabof')  # => true
> > p 'foobar'.all_chars?('abc')    # => false
> > p 'foobar'.all_chars?('')       # => false
> 
>  I'm drawing a blank here with this one.  Why doesn't this work then...
> 
>  irb(main):006:0> r = /\A[oh]*\z/
>  => /\A[oh]*\z/
>  irb(main):007:0> s = "hello, there"
>  => "hello, there"
>  irb(main):008:0> r === s
>  => false

"hello, there" contains letters other than o and h, but your regex
calls for a string consisting of zero or more o's or h's and nothing
else.

I think there might be some confusion as between determining that a
string contains certain characters, and determining that a string
contains *only* certain characters. My understanding was that you
wanted the first, which you could do with tr but I think you'd
probably want the character cluster to be doing the tr'ing:

   "oh".tr("hello, there","").empty?     # true; all letters in "oh"
                                         # are also in "hello, there"
   "hello, there".tr("ho","").empty?     # false

They're both strings, of course, so you can do either with Ara's
or Joel's methods:

   "oh".all_chars?("hello, there")   # true
   "hello, there".all_chars?("oh")   # false

though if it's really the former you want you might want to name it
all_present_in? or something.


David

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