Subj : Re: any function to handle this kind of counting?
To   : comp.programming
From : John W. Krahn
Date : Wed Aug 03 2005 02:00 pm

Rob Thorpe wrote:
> Peter Ammon wrote:
>>Just wait 'til the Perl guy gets here, though!
> 
> I can take on that mantle:
> 
> for(0..($#a<$#b?$#a:$#b)){++$ans{$b[$_]}{$a[$_]};}

Way too much punctuation and not enough whitespace.  :-)

++$ans{ $b[ $_ ], $a[ $_ ] } for 0 .. ( @a < @b ? $#a : $#b );


> This is probably close to the shortest solution that can be done in any
> language - but it's horrible.  Like all the other "terse" solutions it
> misses the point.  In a real program you'll have to document exactly
> why you're doing this operation and how.  Doing so will take a
> significant number of lines.
> 
> For example documenting the perl:
> 
> # Now we have two arrays @a and @b we need to count each
> # char-interger pair across these two arrays.  For example in:
> # @a = ('a', 'b', 'a', 'e', 'a');
> # @b = (  1,   2,   1,   4,   5); there are the pairs
> # (1 ('a' 2))   (2 ('b' 1))   (4 ('e' 1))   (5 ('a' 1))
> for ($i) (0..(($#a < $#b) ? $#a : $#b))  { # Find smallest array
      ^^^^
Syntax error


>     # Make %ans a hash-of-hashes containing the answer
>     ++$ans{$b[$i]}{$a[$i]};
> }

You don't really need a hash of hashes as perl will concatenate comma
separated values in the hash key.

$ perl -e'
@a = qw/ a b a e a /;
@b = qw/ 1 2 1 4 5 /;
$; = "";  # change the subscript separator
++$ans{ $b[ $_ ], $a[ $_ ] } for 0 .. ( @a < @b ? $#a : $#b );
print "$_\t$ans{$_}\n" for sort keys %ans;
'
1a	2
2b	1
4e	1
5a	1



John
-- 
use Perl;
program
fulfillment

.