Trait datafusion_expr::Accumulator

pub trait Accumulator: Send + Sync + Debug {
    fn state(&self) -> Result<Vec<AggregateState>>;
    fn update_batch(&mut self, values: &[ArrayRef]) -> Result<()>;
    fn merge_batch(&mut self, states: &[ArrayRef]) -> Result<()>;
    fn evaluate(&self) -> Result<ScalarValue>;
}

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 aggregate values
• update its state from multiple accumulators’ states via merge_batch
• compute the final value from its internal state via evaluate

Required Methods

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

Returns the state of the accumulator at the end of the accumulation. in the case of an average on which we track sum and n, this function should return a vector of two values, sum and n.

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

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

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

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

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

returns its value based on its current state.

Implementors