R: Create graphs from adjacency lists

graph_from_adj_list {igraph} | R Documentation

## Create graphs from adjacency lists

### Description

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.

### Usage

    graph_from_adj_list(
      adjlist,
      mode = c("out", "in", "all", "total"),
      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.
`mode` | Character scalar, it specifies whether the graph to create is undirected (‘all’ or ‘total’) or directed; and in the latter case, whether it contains the outgoing (‘out’) or the incoming (‘in’) neighbors of the vertices.
`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_from_adj_list` expects `A` included in the neighbors of `B` and `B` to be included in the neighbors of `A`. This argument is ignored if `mode` is `out` or `in`.

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

### Value

An igraph graph object.

### Author(s)

Gabor Csardi csardi.gabor@gmail.com

### See Also

`as_edgelist`

### Examples

    ## Directed
    g <- make_ring(10, directed=TRUE)
    al <- as_adj_list(g, mode="out")
    g2 <- graph_from_adj_list(al)
    graph.isomorphic(g, g2)

    ## Undirected
    g <- make_ring(10)
    al <- as_adj_list(g)
    g2 <- graph_from_adj_list(al, mode="all")
    graph.isomorphic(g, g2)
    ecount(g2)
    g3 <- graph_from_adj_list(al, mode="all", duplicate=FALSE)
    ecount(g3)
    which_multiple(g3)

[Package igraph version 1.3.1 Index]