fillNA method
Fills missing (null) values in the specified column with fillValue.
Implementation
Datacat fillNA(String columnName, dynamic fillValue) {
int index = columns.indexOf(columnName);
if (index == -1) throw ArgumentError('Column "$columnName" not found.');
for (var row in rows) {
if (row[index] == null) {
row[index] = fillValue;
}
}
return this;
}