Trait Accumulator

pub trait Accumulator:
    Send
    + Sync
    + Debug {
    // Required methods
    fn state(&self) -> Result<Vec<Value>>;
    fn update_batch(&mut self, values: &[VectorRef]) -> Result<()>;
    fn merge_batch(&mut self, states: &[VectorRef]) -> Result<()>;
    fn evaluate(&self) -> Result<Value>;
}

An accumulator represents a stateful object that lives throughout the evaluation of multiple rows and generically accumulates values.

An accumulator knows how to:

• update its state from inputs via update_batch
• convert its internal state to a vector of scalar values
• update its state from multiple accumulators’ states via merge_batch
• compute the final value from its internal state via evaluate

Modified from DataFusion.

Required Methods

fn state(&self) -> Result<Vec<Value>>

Returns the state of the accumulator at the end of the accumulation.

fn update_batch(&mut self, values: &[VectorRef]) -> Result<()>

updates the accumulator’s state from a vector of arrays.

fn merge_batch(&mut self, states: &[VectorRef]) -> Result<()>

updates the accumulator’s state from a vector of states.

fn evaluate(&self) -> Result<Value>

returns its value based on its current state.

Implementors