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List:       perl-beginners
Subject:    Re: confusion with splitting columns using [-n, -n] (e.g; my ( $country, $bytes ) = ( split )[ -2, -
From:       "Andy Greenwood" <greenwood.andy () gmail ! com>
Date:       2007-01-30 14:03:43
Message-ID: 3ee9ca710701300603s43d470fbpef49486676cf7b27 () mail ! gmail ! com
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On 1/30/07, Michael Alipio <daem0nb0y@yahoo.com> wrote:
> Hi,
> 
> I have a file that look like this:
> 
> 1668   |  172.194.177.182   |  US    12679172
> 10396   |  64.237.148.157     |  PR     12679172
> 9318   |  211.187.212.242   |  KR    1279172
> 22291   |  66.215.254.186     |  US     1269172
> 22291   |  24.176.212.76       |  US     1679172
> 30225   |  66.147.146.214     |  US     2679172
> 17676   |  221.34.8.92           |  JP      1267173
> 17858   |  125.180.111.187   |  KR    12679172
> 6395   |  67.96.150.40         |  US     12679172
> 17858   |  125.180.193.124   |  KR     12679175
> 3462   |  218.168.176.39     |  TW    12679472
> 9919   |  218.211.204.195   |  TW    12666172
> 9318   |  222.235.22.225     |  KR     12672272
> 9318   |  222.237.14.160     |  KR     12679142
> 
> 
> 
> Six columns including two colums with pipe symbols.
> The goal is to add up the values in the last column that belongs to the same \
> country. That last column are the bytes received by a particular country. So I have \
> to add all bytes received by US, KR, etc. 
> Someone has given me this code:
> 
> open WHOISWITHBYTES, '<', "whois.bytes" or die $!;
> 
> my %data;
> while ( <WHOISWITHBYTES> ) {
> my ( $country, $bytes ) = ( split )[ -2, -1 ];
> $data{ $country } += $bytes;
> }
> 
> print "Country         Total Bytes\n";
> for my $country ( sort { $data{ $b } <=> $data{ $a } } keys %dat
> a ) {
> print "$country              $data{ $country }\n";
> }
> 
> It is working perfectly but now, I need to document this code. Can anyone help me \
> out on understanding this code. 
> I'm particularly confused with the line:
> "my ($country, $bytes) = (split) [-2, -1];
> 
> What does this tells? What does -2 and -1 tells? All I know is that split will \
> output a list containing two values that will be assigned to $country and $bytes \
> for every line of that whois.bytes file. But I'm not sure what those -2,-1 means \
> and how it was able to extract column 5 and 6. I tried looking at perldoc -f split \
> but cannot seem to find the explanation. Are those the LIMIT thing?

(split) gives you an array, and then you are referencing the last two
items. Negative array indecies mean to start that far from the end of
the list, similar to negative character offsets in substr.

> 
> 
> Thanks!
> 
> 
> 
> 
> 
> 
> ____________________________________________________________________________________
>  Any questions? Get answers on any topic at www.Answers.yahoo.com.  Try it now.
> 


-- 
-- 
I'm nerdy in the extreme and whiter than sour cream

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