Struct datafusion_physical_expr::expressions::Median

pub struct Median { /* private fields */ }

MEDIAN aggregate expression. If using the non-distinct variation, then this uses a lot of memory because all values need to be stored in memory before a result can be computed. If an approximation is sufficient then APPROX_MEDIAN provides a much more efficient solution.

If using the distinct variation, the memory usage will be similarly high if the cardinality is high as it stores all distinct values in memory before computing the result, but if cardinality is low then memory usage will also be lower.

Implementations

impl Median

pub fn new( expr: Arc<dyn PhysicalExpr>, name: impl Into<String>, data_type: DataType, distinct: bool ) -> Self

Create a new MEDIAN aggregate function

Trait Implementations

impl AggregateExpr for Median

fn as_any(&self) -> &dyn Any

Return a reference to Any that can be used for downcasting

fn field(&self) -> Result<Field>

the field of the final result of this aggregation.

fn create_accumulator(&self) -> Result<Box<dyn Accumulator>>

the accumulator used to accumulate values from the expressions. the accumulator expects the same number of arguments as expressions and must return states with the same description as state_fields

fn state_fields(&self) -> Result<Vec<Field>>

the fields that encapsulate the Accumulator’s state the number of fields here equals the number of states that the accumulator contains

fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>>

expressions that are passed to the Accumulator. Single-column aggregations such as sum return a single value, others (e.g. cov) return many.

fn name(&self) -> &str

Human readable name such as "MIN(c2)". The default implementation returns placeholder text.

fn order_bys(&self) -> Option<&[PhysicalSortExpr]>

Order by requirements for the aggregate function By default it is None (there is no requirement) Order-sensitive aggregators, such as FIRST_VALUE(x ORDER BY y) should implement this

fn groups_accumulator_supported(&self) -> bool

If the aggregate expression has a specialized GroupsAccumulator implementation. If this returns true, [Self::create_groups_accumulator] will be called.

fn create_groups_accumulator( &self ) -> Result<Box<dyn GroupsAccumulator>, DataFusionError>

Return a specialized GroupsAccumulator that manages state for all groups.

fn reverse_expr(&self) -> Option<Arc<dyn AggregateExpr>>

Construct an expression that calculates the aggregate in reverse. Typically the “reverse” expression is itself (e.g. SUM, COUNT). For aggregates that do not support calculation in reverse, returns None (which is the default value).

fn create_sliding_accumulator( &self ) -> Result<Box<dyn Accumulator>, DataFusionError>

Creates accumulator implementation that supports retract

impl Debug for Median

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq<dyn Any> for Median

fn eq(&self, other: &dyn Any) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.