[Classiccity-pm] basic idiot question

[Jeff Scarbrough]

At 06:51 PM 10/25/2003 -0600, I wrote:

>OK, between the suggestions you and Mark put forth, I think I'm on to 
>something...
>
>So, now I've got one hash for each file, and I ~think~ I know how to get 
>an array of keys...

I do...

>Next trick is to merge the arrays of keys, eliminate duplicates, and sort 
>into numerical/chronological order.  Then I can write a line consisting of 
>the key (the DOY) and the lines of data from each file that match that 
>key, or blank spaces if there is no data in one or more of the files.
>
>The part I need to learn now is how to do the cat |sort...back to Mr. 
>Google's Laboratory...

Simple... I found a bit of code which ends up like this:


@key_list = ();

push @key_list, (keys %array_1);
push @key_list, (keys %array_2);

# Eliminate duplicate entries in key file and sort in ascending order

@key_dup = grep { ++$count{$_} < 2 } @key_list;

@key_sort = sort {$a <=> $b} @key_dup;

Eventually I will come to understand those two statements.  I assume the 
grep goes through and putts only one (<2) occurrrence of the items in 
@key_list into @key_dup.  I'm not sure yet why the sort is written as $a 
<=> $b...  but it works.  I'm learning....


Anyway from there, I can write according to a format statement thusly:


foreach $key_sort(@key_sort) {
   write OUTPUT_FILE;
}

where my format writes the following: $key_sort, 
$array_1{$key_sort},$array_2{$key_sort};

Now, the only problem I have is when data does not exist for the key, I get 
an "uninitialized" kind of error when I write...I need to include something 
on the order of:

if ! $array_1{$key_sort} {
   $array_1{$key_sort} = " ";
}

before I do the write... I'm sure the syntax there is faulty, but that's 
the idea - same for each of the other arrays.  Perhaps a nice single malt 
will aid comprehension....

Progress!

Cheers,
Jeff