# [[.igraph

##### Query and manipulate a graph as it were an adjacency list

Query and manipulate a graph as it were an adjacency list

##### Usage

```
## S3 method for class '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`

- 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`

- ...
- 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.

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##### 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 predessors
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.connected`

, `are_adjacent`

;
`ecount`

, `gsize`

;
`ends`

, `get.edge`

,
`get.edges`

; `get.edge.ids`

;
`gorder`

, `vcount`

;
`head_of`

; `incident_edges`

;
`incident`

; `is.directed`

,
`is_directed`

; `neighbors`

;
`tail_of`

* Documentation reproduced from package igraph, version 1.0.0,
License: GPL (>= 2)
*
### Community examples

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