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Re^2: framework for data parsing

by Narveson (Chaplain)
on Jun 20, 2008 at 21:34 UTC ( #693226=note: print w/replies, xml ) Need Help??

in reply to Re: framework for data parsing
in thread framework for data parsing

I concur wholeheartedly. Use objects and encapsulate the gory details.

My earlier post left the details out in the open. Here's how those details fit into pc88mxer's framework.

For each input file format (i.e. parse specification) you need to be able to create an input source object ...
package RecordParser::FixedWidth; # constructor takes the name of the source file sub new { my ( $class, $source ) = @_;
my $template; my @fields; my @column_specs = lookup_specs($source); for my $column_spec ( @column_specs ) { my ($field, $offset, $width) = @$column_spec{qw(field offset width)}; $template .= "\@${offset}A$width"; push @fields, $field; } open my $reader, '<', $source;
my $obj = { IO => $reader, template => $template, fields_ref => \@fields, }; bless $obj => $class; }
...whose ->next method will produce the next data record (or undef it there isn't any more.)
sub next { my ( $self ) = @_; my ($reader, $template, $fields_ref) = @$self{qw(IO template fields_ref)}; my @fields = @$fields_ref; my $record = <$reader>; return unless defined $record;
my %value_of; my @values = unpack($template, $record); @value_of{@fields} = @values;
The key decision will be what to use for your data record object. A good generic choice is to use a hash-ref.
return \%value_of; }

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Re^3: framework for data parsing
by sardare (Initiate) on Jun 22, 2008 at 05:17 UTC
    Thanks for the valuable suggestions. Another challenge to this problem is that the data files are multi-line records. For example, if a line or row is a parent, then it is followed by a number of component rows. I am thinking of extending the basic data parser to multi-row parser and return the complete parent record (containing its component records) to the client for each next() call. What do you think about this approach? Another issue is validation. I noticed that unpack fails silently if there is a problem in parsing. So I would like to set up some sort of validation for the lines too. That should probably go in the spec for the record and be specified as a regex pattern.

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