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data:list:union

Coalesces two lists into one item per key, preferring the first list. Items pair up through the configured key paths, A's item is taken wherever a key appears in both, and B fills the keys A has nothing for. That is the link a precedence chain is built from, so a policy such as approved over published over base is a union of a union rather than a query that has to know the policy. Neither list may repeat a key, and nothing is written anywhere.

Options

Name	Type	Description
`a`	`[]map[string]any`	The preferred list, whose item wins wherever a key appears in both
`b`	`[]map[string]any`	The filling list, whose item is taken only for a key A does not carry
`keys`	`[]string`	The dotted paths whose values identify the same item in both lists

Outputs

Name	Type	Description
`items`	`[]map[string]any`	The union, in A's order followed by the keys only B carries
`counts`	`ListUnionCounts`	The size of the union and each side's contribution
↳ `items`	`int`
↳ `from_a`	`int`
↳ `from_b`	`int`

Example

name: Resolve a translation by precedence
actions:
  - name: stable_head
    component: data:list:union
    vars:
      a: "{{ var.approved }}"
      b: "{{ var.published }}"
      keys: [key_id, variant]
  - name: stable
    component: data:list:union
    vars:
      a: "{{ stable_head.items }}"
      b: "{{ var.base_values }}"
      keys: [key_id, variant]

outputs:
  items: "{{ stable.items }}"
  counts: "{{ stable.counts }}"

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