# disjoint_union

##### Disjoint union of graphs

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

- Keywords
- graphs

##### Usage

`disjoint_union(...)`x %du% y

##### Arguments

- …
Graph objects or lists of graph objects.

- x, y
Graph objects.

##### Details

`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.

##### Value

A new graph object.

##### Examples

```
# NOT RUN {
## 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]
print_all(g1 %du% g2)
# }
```

*Documentation reproduced from package igraph, version 1.2.3, License: GPL (>= 2)*