where method
Filter rows matching predicate. Returns new CsvTable.
Implementation
CsvTable where(bool Function(CsvRow row) test) {
final headerMap = buildHeaderMap();
final filtered = rawData.where((r) => test(CsvRow(r, headerMap))).toList();
return CsvTable.internal(
List<String>.from(headers),
filtered.map((r) => List<dynamic>.from(r)).toList(),
);
}