coalesce
Return a value based on the first traversal that has an element.
Synopsis
coalesce(traversal,traversal\_1, ...)
Description
The coalesce() step evaluates the provided traversals in order and returns the first traversal that emits at least one element.
Examples
Create a list of each person and their mean average of stars given for recipe reviews, using coalesce() to either print the mean or print a constant zero value if no reviews are found:
"g.V().hasLabel('person').as('person','starCount').
select('person','starCount').
by('name').
by(coalesce(outE('reviewed').values('stars'),constant(0)).mean()).
order().by(select('starCount'), decr)"
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