fieldPostings method
Filters the PostingsMap by zone names.
Returns a subset of the PostingsMap instance that only contains entries
where a zone name in fields
has a key in any document's postings the
entry's postings lists.
Implementation
PostingsMap fieldPostings(Iterable<String> fields) => PostingsMap.from(this)
..removeWhere((key, value) {
final docFields = <String>[];
for (final doc in value.values) {
docFields.addAll(doc.keys);
}
return docFields.toSet().intersection(fields.toSet()).isEmpty;
});