# difference.igraph

From igraph v1.0.0
by Gabor Csardi

##### Difference of graphs

The difference of two graphs are created.

- Keywords
- graphs

##### Usage

```
## S3 method for class '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 - ...
- 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

```
## 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 1.0.0, License: GPL (>= 2)*

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