The difference of two graphs are created.

## 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.

## See also

Other functions for manipulating graph structure:
`+.igraph()`

,
`add_edges()`

,
`add_vertices()`

,
`complementer()`

,
`compose()`

,
`connect()`

,
`contract()`

,
`delete_edges()`

,
`delete_vertices()`

,
`difference()`

,
`disjoint_union()`

,
`edge()`

,
`igraph-minus`

,
`intersection.igraph()`

,
`intersection()`

,
`path()`

,
`permute()`

,
`rep.igraph()`

,
`reverse_edges()`

,
`simplify()`

,
`union.igraph()`

,
`union()`

,
`vertex()`

## Author

Gabor Csardi csardi.gabor@gmail.com

## 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
print_all(G)
#> IGRAPH e5cfa2f UN-- 11 15 --
#> + attr: name_1 (g/c), name_2 (g/c), mutual (g/l), circular (g/l), mode
#> | (g/c), center (g/n), name (v/c)
#> + edges (vertex names):
#> a -- b, j
#> b -- a, c, k
#> c -- b, d
#> d -- c, e, k
#> e -- d, f
#> f -- e, g, k
#> g -- f, h
#> h -- g, i, k
#> i -- h, j
#> j -- a, i, k
#> k -- b, d, f, h, j
plot(G, layout = layout_nicely(wheel))
```