@Override
    public Expression aggregate() {
        return Expression.variable(baseAttributes[0].getName());
    }
{@link IncrementalAttributeAggregator} to calculate maximum value based on an event attribute.
modules/siddhi-core/src/main/java/io/siddhi/core/query/selector/attribute/aggregator/incremental/MaxIncrementalAttributeAggregator.java