Re: Return values from MARC::Record

[Paul Hoffman]

On Friday, November 7, 2003, at 08:23  AM, Paul Hoffman wrote:

On Thursday, November 6, 2003, at 08:45  PM, Leif Andersson wrote:

Assume we have a record with two 035 fields
035 -- $91234567
035 -- $a(XX)12345678
Now, this code will get the 035 $9 subfield:
$subfield  = eval { $record->field('035')->subfield('9') };
@subfields = eval { $record->field('035')->subfield('9') };
But this it will fail getting 035 $a
$subfield  = eval { $record->field('035')->subfield('a') };
@subfields = eval { $record->field('035')->subfield('a') };
I don't see how this can be.  Am I missing something?
D'oh!  Of course it fails to find the 035 $a subfield -- the call to 
$record->field('035') in scalar context only returns the *first* 035 
field.

My bad.

As for the problem at hand, map and grep are your friends:

   my @fields = $record->field('035');
      # --> list of all 035 fields
   my @possible_subfields = map { $_->subfield('a') } @fields;
      # --> list of results of calling subfield('a') on all 035 fields
   my @subfields = grep { defined } @possible_subfields;
      # --> existing 035 $a subfields only
Or, more succinctly:

   @subfields = grep { defined } map { $_->subfield('a') } @fields;

Most Perl programmers are familiar with this idiom, so I wouldn't worry 
about it being hard to understand.

Paul.

-----Ursprungligt meddelande-----
Från: Paul Hoffman [mailto:[EMAIL PROTECTED]
Skickat: den 6 november 2003 22:30
Till: Leif Andersson
Kopia: [EMAIL PROTECTED]
Ämne: Re: Return values from MARC::Record
On Thursday, November 6, 2003, at 01:14  PM, Leif Andersson wrote:

With the same BAD record we try $subfield = eval {
$record->field($tag)->subfield($sub) }
This is the only case where we have to put the code in eval.
Should MARC:: take care of the eval for us? I am beginning to think 
so.
No, it can't.  Just add your own error checking, something like this
for example:
    my $field = $record->field($tag) || die "No tag '$tag' in record";
    $subfield = $field->subfield($sub);
MARC::Record::field has no way of knowing that your code will invoke
the method 'subfield' on the value it returns.  You could also do it
like this if you want to keep things concise:
    $subfield = ($record->field($tag) || die "No tag '$tag' in
record")->subfield($sub);
But that's getting a wee bit obfuscated.

Paul.
--
Paul Hoffman :: Taubman Medical Library :: Univ. of Michigan
[EMAIL PROTECTED] :: [EMAIL PROTECTED] :: http://www.nkuitse.com/

--
Paul Hoffman :: Taubman Medical Library :: Univ. of Michigan
[EMAIL PROTECTED] :: [EMAIL PROTECTED] :: http://www.nkuitse.com/