From: Gawnsoft <xlucid@...>
Date: 2003-08-02T01:33:07+09:00
Subject: Re: A bundle of newbie queries

On Sat, 2 Aug 2003 00:44:24 +0900, Brian Candler <B.Candler@pobox.com>
wrote (more or less):

>On Sat, Aug 02, 2003 at 12:12:39AM +0900, Gawnsoft wrote:
>> On Fri, 1 Aug 2003 21:30:19 +0900, dblack@superlink.net wrote (more or
>> less):
>> 
>> >On Fri, 1 Aug 2003, Gawnsoft wrote:
>> >>...
>> >>    aDictionary = Hash.new(0)
>> >>
>> >>    aFile.each_line { | eachLine | aDictionary[ /[0-9.]+/ ] =
>> >> aDictionary[ /[0-9.]+/ ] + 1 if
>> >> eachLine.include?("plastic_1.1_lite-UMLtool-fw.exe") }
>> >>
>> >
>> >Yes, you can use a regex as a key, but in your example, you're not
>> >doing anything else with it :-)  You'd get the same results with:
>> >
>> >   dict[/blah/] = dict[/blah/] + 1
>> 
>> It was in IRB, so once I had the dictionary populated, I was also then
>> able to 
>>    aDictionary.each_value { | entry | puts entry }
>> to see how often some people had downloaded the file and the like, so
>> it wasn't entrirely wasted.
>
>It seems you are doing something strange. Consider these examples:
>
>   h = {}
>   h[/blah/] = 1
>   h[/blah/] = 1
>   h[/blah/] = 1
>   p h             #>> {/blah/=>1, /blah/=>1, /blah/=>1}
>
>In other words, it looks like you are populating the hash with three
>different Regex objects as the key. That's not very useful.

You're absolutely right - I pasted in the wrong bits of code!
(alternative phrasing, I pasted in bits of wrong code)  Aargh.  The
corrected code reads:

   aFile.each_line { | line | aDictionary[line.slice(/[0-9.]+/)] =
aDictionary[line.slice(/[0-9.]+/)] + 1 if eachLine.include?("plastic")
}

Thanks for pointing this out, and sorry to mislead.

>Just to confuse things a bit:
>
>   h = Hash.new(0)
>   3.times { h[/blah/] = h[/blah/] + 1 }
>   p h             #>> {/blah/=>1}
>
>(i.e. there are only two /blah/ objects this time: one is used as the key on
>the left-hand side, and one as the key on the right-hand side)
>
>I think what you want is:
>
>   h = Hash.new(0)
>   str = "wibble 1.2.3.4 bibble"
>
>   /([0-9.]+)/ =~ str
>   h[$1] += 1  if  $1
>
>   p h             #>> {"1.2.3.4"=>1}
>
>You also have to beware of free-standing regular expressions, because they
>have some perlish side-effects in certain circumstances (inside
>conditionals, I think):
>
>    gets            # assigns to $_ as a side-effect
>    if /([0-9.]+)/  # matches against $_ by default
>      h[$1] += 1
>    end
>
>This usage is uncouth and deprecated.
>
>> >or even:
>> >
>> >   dict[/blah/] = dict["hello!"] + 1
>> 
>> Hmmm - wouldn't this result in aDictionary having an entry with a key
>> of "hello!" and so through my count of IP numbers off by one?
>
>No - unlike Perl, reading from a hash element which does not exist does not
>cause that element to be created. Example:
>
>     h = Hash.new(99)
>     p h["foo"]         #>> 99      -- default value returned
>     p h                #>> {}      -- but the hash was not modified
>
>Regards,
>
>Brian.

Cheers, 
   Euan
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