[lug] perl hash and array assignments in a loop

[Elyse M. Grasso]

On Friday 16 November 2007, karl horlen wrote:
> I haven't programmed perl in awhile and can't find the
> answer to what should be a pretty simple operation.
> 
> I read file input line by line in a loop.  I split the
> line fields out to an array called @tokens.  I know
> that array is being set correctly via a test print
> statement.
> 
> The problem comes in when I try to assign the array to
> a hash key/variable.  After searching for a long time
> it looks like perl requires that I assign an array as
> a
> reference to the hash key.  I believe that part is
> working by debug print statements.
> 
> However when it comes time to print the array VALUES
> as output, I either print the array value count or the
> array reference address and never the values
> contained in the array.
> 
> 1) How do I output the array values contained in the
> hash key in a single print statement?  Similar to how
> you use 'print @tokens' for a standard array.
> 
> 2) I know this will be soon on deck. How do I
> individually print each hash key array value
> separately using a loop?  I can handle the loop, I
> just
> need to know the convoluted syntax  to access the hash
> key array values one by one.
> 
> My very simplified code snippet that isn't working
> (stuff left out)
> 
> LOOP
> 
>   my @tokens = split(' ');
> 
>   # this works!
>   #print "@tokens";
> 
>   # assign by reference
>   $report{$id}{$dateinfo} = \@tokens;
> 
>   # TRY TO PRINT as an array 
>   # WRONG! this prints the count of array 
>   # values but not the values themselves!
>   print "dateinfo is :" . @{$report{$id}{$dateinfo}} .
> "\n";
> 
>   # TRY TO PRINT as a scalar
>   # WRONG!  this prints the array ref not the
> values!!! -> dateinfo is :ARRAY(0x8f865fc)
>   print "dateinfo is :" . $report{$id}{$dateinfo} .
> "\n";
> 
> END LOOP
> 
> Also.  How would I add a scalar variable that keeps a
> running count of records that have the same date?
> 
> This actually works:
> 
>   $record{$id}{$dateinfo}++;
> 
> But if I assign an array to hold the field values to
> that $dateinfo key as described above and then
> increment a count on it, I will overwrite the array
> stored in the hash key.
> 
> That means I need to go with another hash level but
> I'm getting more confused with the perl syntax.  I
> imagine it would look something like this:
> 
>   $record{$id}{$dateinfo}$count++;
>   $record{$id}{$dateinfo}@fields;
> 
> Any Perl pros out there?
> 
> 
> 
>       
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print "dateinfo is :" .join (/ /, @{$report{$id}{$dateinfo}});

or 
print "dateinfo is :";
foreach my $item (@{$report{$id}{$dateinfo}}){
	print $item;
}

etc.

You need to access it in list mode not scalar mode.

-- 
Elyse Grasso

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