transition.merge()

transition.merge(other)

Returns a new transition merging this transition with the specified other transition, which must have the same id as this transition. The returned transition has the same number of groups, the same parents, the same name and the same id as this transition. Any missing (null) elements in this transition are filled with the corresponding element, if present (not null), from the other transition.

This method is equivalent to deriving the selection for this transition via transition.selection, merging with the selection likewise derived from the other transition via selection.merge, and then creating a new transition via selection.transition:

transition
  .selection()
  .merge(other.selection())
  .transition(transition)