hugo/docs/content/en/functions/symdiff.md

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symdiff	`collections.SymDiff` (alias `symdiff`) returns the symmetric difference of two collections.	functions	docs parent functions	collections intersect union complement	COLLECTION | symdiff COLLECTION

Example:

{{ slice 1 2 3 | symdiff (slice 3 4) }}

The above will print [1 2 4].

Also see https://en.wikipedia.org/wiki/Symmetric_difference