# graph_from_adj_list: Create graphs from adjacency lists In igraph: Network Analysis and Visualization

## 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

 ```1 2 3 4 5``` ```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

`as_edgelist`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15``` ```## Directed g <- make_ring(10, dir=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) ```