Reshapes

Union

Combine Spaces and collapse rows with the same exact key.

Union materializes several input Spaces into one output Space and merges rows sharing the declared key.

Worked example

Union(
    name="combine-and-deduplicate",
    input_spaces=("web-products", "store-products"),
    output_space="products",
    key="sku",
    merge_policy={"inventory": "sum", "tags": "union"},
)

Parameter	Default	Meaning
`input_spaces`	required	The Space or Spaces read by the reshape.
`name`	required	A stable node name shown in the pipeline and session.
`output_space`	required	The combined output Space.
`key`	id	Field or fields used for exact grouping. Every key field must exist in every input Space.
`merge_policy`	preserve	Per-field rules such as sum, min, max, union, last, or a callable.

Output

One merged row per distinct key.

Design guidance

Union is exact deduplication and group-by aggregation. Use SemCluster only when two different keys may still denote the same semantic value. When later semantic work must preserve every source identity, union the identity-list field explicitly, keep that list out of model evidence, and map the semantic result back afterward.