# difference.igraph

##### Difference of graphs

The difference of two graphs are created.

- Keywords
- graphs

##### Usage

```
# S3 method for igraph
difference(big, small, byname = "auto", ...)
```

##### Arguments

- big
The left hand side argument of the minus operator. A directed or undirected graph.

- small
The right hand side argument of the minus operator. A directed ot undirected graph.

- byname
A logical scalar, or the character scalar

`auto`

. Whether to perform the operation based on symbolic vertex names. If it is`auto`

, that means`TRUE`

if both graphs are named and`FALSE`

otherwise. A warning is generated if`auto`

and one graph, but not both graphs are named.- ...
Ignored, included for S3 compatibility.

##### Details

`difference`

creates the difference of two graphs. Only edges
present in the first graph but not in the second will be be included in the
new graph. The corresponding operator is %m%.

If the `byname`

argument is `TRUE`

(or `auto`

and the graphs
are all named), then the operation is performed based on symbolic vertex
names. Otherwise numeric vertex ids are used.

`difference`

keeps all attributes (graph, vertex and edge) of the
first graph.

Note that `big`

and `small`

must both be directed or both be
undirected, otherwise an error message is given.

##### Value

A new graph object.

##### Examples

```
# NOT RUN {
## Create a wheel graph
wheel <- union(make_ring(10),
make_star(11, center=11, mode="undirected"))
V(wheel)$name <- letters[seq_len(vcount(wheel))]
## Subtract a star graph from it
sstar <- make_star(6, center=6, mode="undirected")
V(sstar)$name <- letters[c(1,3,5,7,9,11)]
G <- wheel %m% sstar
str(G)
plot(G, layout=layout_nicely(wheel))
# }
```

*Documentation reproduced from package igraph, version 1.0.1, License: GPL (>= 2)*