Function.ScalarVector

Function

Creates a scalar function that invokes a vector function behind the scenes, enabling batch processing when applied row-by-row across a table.

Syntax

Function.ScalarVector(scalarFunctionType as type, vectorFunction as function) as function

Parameters

Name	Type	Required	Description
`scalarFunctionType`	`type`	Yes	The function type defining the parameter names, types, and return type for the scalar function.
`vectorFunction`	`function`	Yes	A function that receives a table of inputs (one row per call) and returns a list of results, one per input row.

Return Value

function — A scalar function matching the specified type signature that delegates to the vector function for batch processing.

Remarks

Function.ScalarVector creates a scalar function (one that processes a single row) backed by a vector function (one that processes many rows at once). When the scalar function is applied row-by-row — for example, via Table.AddColumn — the engine automatically batches the calls and passes all inputs to the vectorFunction at once, rather than invoking the scalar function individually for each row.

How it works

1. The returned function appears as a normal scalar function matching scalarFunctionType. 2. When called individually, the vectorFunction receives a single-row table and should return a single-element list. 3. When the scalar function is used in a row-by-row context like Table.AddColumn, the engine collects all input rows into a table and passes them to vectorFunction in one batch (or in chunks).

vectorFunction contract

Input: A table whose columns match the parameter names and positions of scalarFunctionType. Each row represents one call to the scalar function.
Output: A list with the same length as the input table. Each item is the result for the corresponding input row.
The input table is streamed, so vectorFunction should process data in chunks and must not enumerate the input table more than once.

Use cases

API batching — calling an external API with batched requests instead of one-by-one.
Expensive computations — processing multiple inputs together for efficiency.
Custom connector optimization — enabling bulk operations that are more efficient than individual calls.

Examples

Example 1: Batch-multiply two columns

let
    MultiplyScalar = (left, right) => left * right,
    MultiplyVector = (input) =>
        Table.TransformRows(input, each [left] * [right]),
    Multiply = Function.ScalarVector(
        type function (left as number, right as number) as number,
        MultiplyVector
    ),
    Source = Table.FromRecords({
        [a = 1, b = 2],
        [a = 3, b = 4]
    }),
    Result = Table.AddColumn(Source, "Product", each Multiply([a], [b]))
in
    Result

Output

	a	b	Product
1	1	2	2
2	3	4	12

Compatibility

✓ Power BI Desktop✓ Power BI Service✓ Excel Desktop✓ Excel Online✓ Dataflows✓ Fabric Notebooks