# Graphs from adjacency lists

From igraph v0.5.5-3
by Gabor Csardi

##### Create graphs from adjacency lists

An adjacency list is a list of numeric vectors, containing the neighbor vertices for each vertex. This function creates an igraph graph object from such a list.

- Keywords
- graphs

##### Usage

`graph.adjlist(adjlist, directed = TRUE, duplicate = TRUE)`

##### Arguments

- adjlist
- The adjacency list. It should be consistent, i.e. the maximum throughout all vectors in the list must be less than the number of vectors (=the number of vertices in the graph). Note that the list is expected to be 0-indexed.
- directed
- Logical scalar, whether or not to create a directed graph.
- duplicate
- Logical scalar. For undirected graphs it gives
whether edges are included in the list twice. E.g. if it is
`TRUE`

then for an undirected`{A,B}`

edge`graph.adjlist`

expects`A`

included in the neigh

##### Details

Adjacency lists are handy if you intend to do many (small) modifications to a graph. In this case adjacency lists are more efficient than igraph graphs.

The idea is that you convert your graph to an adjacency list by
`get.adjlist`

, do your modifications to the graphs and
finally create again an igraph graph by calling `graph.adjlist`

.

##### Value

- An igraph graph object.

##### See Also

##### Examples

```
## Directed
g <- graph.ring(10, dir=TRUE)
al <- get.adjlist(g, mode="out")
g2 <- graph.adjlist(al)
graph.isomorphic(g, g2)
## Undirected
g <- graph.ring(10)
al <- get.adjlist(g)
g2 <- graph.adjlist(al, dir=FALSE)
graph.isomorphic(g, g2)
ecount(g2)
g3 <- graph.adjlist(al, dir=FALSE, duplicate=FALSE)
ecount(g3)
is.multiple(g3)
```

*Documentation reproduced from package igraph, version 0.5.5-3, License: GPL (>= 2)*

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