igraph (version 1.0.1)

disjoint_union: Disjoint union of graphs


The union of two or more graphs are created. The graphs are assumed to have disjoint vertex sets.



x %du% y



Graph objects.

Graph objects or lists of graph objects.


A new graph object.


disjoint_union creates a union of two or more disjoint graphs. Thus first the vertices in the second, third, etc. graphs are relabeled to have completely disjoint graphs. Then a simple union is created. This function can also be used via the %du% operator.

graph.disjont.union handles graph, vertex and edge attributes. In particular, it merges vertex and edge attributes using the basic c() function. For graphs that lack some vertex/edge attribute, the corresponding values in the new graph are set to NA. Graph attributes are simply copied to the result. If this would result a name clash, then they are renamed by adding suffixes: _1, _2, etc.

Note that if both graphs have vertex names (ie. a name vertex attribute), then the concatenated vertex names might be non-unique in the result. A warning is given if this happens.

An error is generated if some input graphs are directed and others are undirected.


## A star and a ring
g1 <- make_star(10, mode="undirected")
V(g1)$name <- letters[1:10]
g2 <- make_ring(10)
V(g2)$name <- letters[11:20]
str(g1 %du% g2)
# }