Difference

The Difference operator calculates sequential differences between pairs of numeric values in a data stream. It maintains a buffer of size 2 to compute differences between consecutive values.

Configuration

Required Parameters

• id: Unique identifier for the operator
• use_oldest_time: (Optional) Controls timestamp of output messages
  • true: Use newer message's timestamp
  • false: Use older message's timestamp

Example Configuration

{
  "id": "diff1",
  "use_oldest_time": true
}

Port Configuration

Inputs

• Port 0: Accepts NumberData messages

Outputs

• Port 0: Emits NumberData messages with computed differences

Operation

The operator emits messages with values calculated as:

output_value = newest_value - oldest_value

Message Flow Example

Time	Input Value	Output Value	Notes
1	10.0	-	First value buffered
2	15.0	5.0	First difference (15.0 - 10.0)
4	12.0	-3.0	Next difference (12.0 - 15.0)
5	20.0	8.0	Next difference (20.0 - 12.0)

Key Characteristics

• Buffer size: 2 messages
• Output timing: Configurable via use_oldest_time
• Processing: O(1) per message
• Memory usage: O(1) fixed
• Must receive 2 messages before first output

Error Handling

The operator will throw exceptions for:

• Invalid message types on input port
• Type mismatches on input

Use Cases

Ideal for:

• Rate of change calculations
• Delta detection
• Trend analysis
• Signal differentiation

Example Usage

// Create operator using newer message timestamps
auto diff = std::make_shared<Difference>("diff1", true);
auto col = std::make_shared<Collector>("c", std::vector<std::string>{"number"});
diff->connect(col, 0, 0);

// Process some values
diff->receive_data(create_message<NumberData>(1, NumberData{10.0}), 0);
diff->receive_data(create_message<NumberData>(2, NumberData{15.0}), 0);
diff->execute();

// Access difference via the downstream Collector
const auto& output = col->get_data_queue(0);
// Output will contain a message with value 5.0 at time 2