getKeywordsPostings method
Filters the KeywordPostingsMap by keywords.
Returns a subset of the KeywordPostingsMap instance that only contains
entires with a key in the keywords
collection.
Implementation
KeywordPostingsMap getKeywordsPostings(Iterable<String> keywords) {
final newEntries =
entries.where((element) => keywords.contains(element.key));
final KeywordPostingsMap retVal = {}..addEntries(newEntries);
return retVal;
}