Hash value overwrite due to similar keys? - perl

Question

I want to map data from a German data structure to an English one.
For that I use a hash which holds the German words as keys and the English ones as values ($mapping_table).
The data are stored in an array of hashes ($data). The keys are the German words which have to be replaced by English ones. The values are the data which shall stay unchanged.
To do the mapping I have written the following code:
my $mapping_table = {
'Exemplare' => 'copies',
'Seiten' => 'pages',
'Statushinweis' => 'status',
'Serie von' => 'number_of',
'ISBN/Barcode-Nr.' => 'ISBN_barcode',
'Status' => 'status',
};
my $data = [
{
'Exemplare' => '1',
'Seiten' => '0',
'Statushinweis' => 'Statushinweis',
'ISBN/Barcode-Nr.' => '3-551-01561-9',
'Serie von' => '4',
'Status' => 'Gesucht'
},
{
'Exemplare' => '4',
'Seiten' => '111',
'Statushinweis' => '',
'ISBN/Barcode-Nr.' => '3-551-01561-9',
'Serie von' => '4',
'Status' => 'Vorhanden'
}
];
my $mapped_data = [];
foreach my $issue ( #$data ) {
my %tmp_hash;
foreach my $key (sort keys %$mapping_table) {
$tmp_hash{$mapping_table->{$key}} = $issue->{$key};
}
push #$mapped_data, \%tmp_hash;
}
print Dumper $mapped_data;
The result of the dump surprises me a lot.
$VAR1 = [
{
'number_of' => '4',
'copies' => '1',
'status' => 'Statushinweis',
'ISBN_barcode' => '3-551-01561-9',
'pages' => '0'
},
{
'pages' => '111',
'ISBN_barcode' => '3-551-01561-9',
'status' => '',
'copies' => '4',
'number_of' => '4'
}
];
It can be seen that the values of the keys 'status' hold those of the keys 'Statushinweis' whereas these keys got completely lost.
I tried to figure out why this happens with the help of Google and the debugger but failed (maybe to obvious to be seen?).
Maybe I should mention that I work with strawberry perl 5.26.1 on Win7.
Any idea what I did wrong and how to fix it?
Thx in advance.

Answer 1

Your mapping table needs to support bi-directional mapping. Currently, you cannot map from "value" (the, well, value) to "Status" or "Statushinweis", because both keys have the same value. If you can choose your keys freely, rename one of them, for instance:
my $mapping_table = {
'Exemplare' => 'copies',
'Seiten' => 'pages',
'Statushinweis' => 'statushint', // <- change here
'Serie von' => 'number_of',
'ISBN/Barcode-Nr.' => 'ISBN_barcode',
'Status' => 'status',
};
my $data = [
{
'Exemplare' => '1',
'Seiten' => '0',
'Statushinweis' => 'Statushinweis',
'ISBN/Barcode-Nr.' => '3-551-01561-9',
'Serie von' => '4',
'Status' => 'Gesucht'
},
{
'Exemplare' => '4',
'Seiten' => '111',
'Statushinweis' => '',
'ISBN/Barcode-Nr.' => '3-551-01561-9',
'Serie von' => '4',
'Status' => 'Vorhanden'
}
];