Used to 'transfer' information from nodes to other nodes across specific predicates, either in an outward direction (along the edge direction) or inward (against the edge direction). Returns a node-property column; intended to be used with mutate() on nodes.
transfer(colname = NULL, over, direction = "out")Vector or list, with one entry per node.
The return value will be either a list, or if the result would be a list with all length-1 or length-0 elements, a vector with 0-length elements replaced by NA. Practically, this results in a list when necessary and a vector otherwise.