Query and manipulate a graph as it were an adjacency list

## Usage

```
# S3 method for igraph
[[(x, i, j, from, to, ..., directed = TRUE, edges = FALSE, exact = TRUE)
```

## Arguments

- x
The graph.

- i
Index, integer, character or logical, see details below.

- j
Index, integer, character or logical, see details below.

- from
A numeric or character vector giving vertex ids or names. Together with the

`to`

argument, it can be used to query/set a sequence of edges. See details below. This argument cannot be present together with any of the`i`

and`j`

arguments and if it is present, then the`to`

argument must be present as well.- to
A numeric or character vector giving vertex ids or names. Together with the

`from`

argument, it can be used to query/set a sequence of edges. See details below. This argument cannot be present together with any of the`i`

and`j`

arguments and if it is present, then the`from`

argument must be present as well.- ...
Additional arguments are not used currently.

- directed
Logical scalar, whether to consider edge directions in directed graphs. It is ignored for undirected graphs.

- edges
Logical scalar, whether to return edge ids.

- exact
Ignored.

## Details

The double bracket operator indexes the (imaginary) adjacency list of the graph. This can used for the following operations:

Querying the adjacent vertices for one or more vertices:

`graph[[1:3,]] graph[[,1:3]]`

The first form gives the successors, the second the predecessors or the 1:3 vertices. (For undirected graphs they are equivalent.)

Querying the incident edges for one or more vertices, if the

`edges`

argument is set to`TRUE`

:`graph[[1:3, , edges=TRUE]] graph[[, 1:3, edges=TRUE]]`

Querying the edge ids between two sets or vertices, if both indices are used. E.g.

`graph[[v, w, edges=TRUE]]`

gives the edge ids of all the edges that exist from vertices \(v\) to vertices \(w\).

The alternative argument names `from`

and `to`

can be used
instead of the usual `i`

and `j`

, to make the code more
readable:

```
graph[[from = 1:3]]
graph[[from = v, to = w, edges = TRUE]]
```

‘`[[`

’ operators allows logical indices and negative indices
as well, with the usual R semantics.

Vertex names are also supported, so instead of a numeric vertex id a
vertex can also be given to ‘`[`

’ and ‘`[[`

’.

## See also

Other structural queries:
`[.igraph()`

,
`adjacent_vertices()`

,
`are_adjacent()`

,
`ends()`

,
`get.edge.ids()`

,
`gorder()`

,
`gsize()`

,
`head_of()`

,
`incident_edges()`

,
`incident()`

,
`is_directed()`

,
`neighbors()`

,
`tail_of()`