private String generateKey(StreamEvent event) {      // for performance reason if its all attribute we don't do
        // the attribute list check
        StringBuilder stringBuilder = new StringBuilder();
        if (variableExpressionExecutors.length == 0) {
            for (Object data : event.getOutputData()) {
                stringBuilder.append(data);
            }
        } else {
            for (VariableExpressionExecutor executor : variableExpressionExecutors) {
                stringBuilder.append(event.getAttribute(executor.getPosition()));
            }
        }
        return stringBuilder.toString();
    }
Implementation of {@link WindowProcessor} which represent a Window operating based on event frequency.
modules/siddhi-core/src/main/java/io/siddhi/core/query/processor/stream/window/LossyFrequentWindowProcessor.java