Struct LambdaArgument 

pub struct LambdaArgument { /* private fields */ }

A lambda argument to a HigherOrderFunction

Implementations

impl LambdaArgument

pub fn new( params: Vec<Arc<Field>>, body: Arc<dyn PhysicalExpr>, captures: Option<RecordBatch>, ) -> LambdaArgument

pub fn evaluate( &self, args: &[&dyn Fn() -> Result<Arc<dyn Array>, DataFusionError>], spread_captures: impl FnOnce(&[Arc<dyn Array>]) -> Result<Vec<Arc<dyn Array>>, DataFusionError>, ) -> Result<ColumnarValue, DataFusionError>

Evaluate this lambda args should evaluate to the value of each parameter of the correspondent lambda returned in HigherOrderUDFImpl::lambda_parameters.

spread_captures is responsible for transforming the captured column arrays so they align with the evaluation batch. Captures are snapshotted from the outer batch at construction time, giving one value per outer row, but the function may evaluate the lambda body over a batch with a different number of rows. It is the function’s responsibility to provide the appropriate spread_captures closure to expand (or otherwise reshape) the captures to match.

Taking as an example the following table:

CREATE TABLE t (arr INT[], a INT) AS VALUES
  ([1, 2, 3], 10),
  ([],        20),
  ([4],       30);

SELECT array_transform(arr, v -> v + a) from t would execute over three outer rows:

arr (ListArray):  [[1, 2, 3], [], [4]]   -- 3 outer rows, 4 total elements
a   (captured):   [10,        20,  30]   -- one value per outer row

array_transform flattens the list elements into a single batch of 4 rows, so spread_captures must repeat/drop captured values to match:

v (flattened args): [1,  2,  3,  4]
a (spread):         [10, 10, 10, 30]  -- 10 repeated for 3 elements in row 0,
                                       -- 20 dropped for the empty sublist in row 1,
                                       -- 30 once for the single element in row 2

The lambda body v + a then evaluates element-wise over these 4-row arrays, producing [11, 12, 13, 34], which array_transform reassembles into [[11, 12, 13], [], [34]].

If the lambda has no captures, spread_captures is never called.

Trait Implementations

impl Clone for LambdaArgument

fn clone(&self) -> LambdaArgument

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for LambdaArgument

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

Formats the value using the given formatter.