R: Convert between directed and undirected graphs

as.directed {igraph} | R Documentation

## Convert between directed and undirected graphs

### Description

`as.directed` converts an undirected graph to directed, `as.undirected` does the opposite, it converts a directed graph to undirected.

### Usage

    as.directed(graph, mode = c("mutual", "arbitrary"))

    as.undirected(
      graph,
      mode = c("collapse", "each", "mutual"),
      edge.attr.comb = igraph_opt("edge.attr.comb")
    )

### Arguments

`graph` | The graph to convert.
`mode` | Character constant, defines the conversion algorithm. For `as.directed` it can be `mutual` or `arbitrary`. For `as.undirected` it can be `each`, `collapse` or `mutual`. See details below.
`edge.attr.comb` | Specifies what to do with edge attributes, if `mode="collapse"` or `mode="mutual"`. In these cases many edges might be mapped to a single one in the new graph, and their attributes are combined. Please see `attribute.combination` for details on this.

### Details

Conversion algorithms for `as.directed`:

"arbitrary"

  The number of edges in the graph stays the same, an arbitrarily directed edge is created for each undirected edge.

"mutual"

  Two directed edges are created for each undirected edge, one in each direction.

Conversion algorithms for `as.undirected`:

"each"

  The number of edges remains constant, an undirected edge is created for each directed one, this version might create graphs with multiple edges.

"collapse"

  One undirected edge will be created for each pair of vertices which are connected with at least one directed edge, no multiple edges will be created.

"mutual"

  One undirected edge will be created for each pair of mutual edges. Non-mutual edges are ignored. This mode might create multiple edges if there are more than one mutual edge pairs between the same pair of vertices.

### Value

A new graph object.

### Author(s)

Gabor Csardi csardi.gabor@gmail.com

### See Also

`simplify` for removing multiple and/or loop edges from a graph.

### Examples

    g <- make_ring(10)
    as.directed(g, "mutual")
    g2 <- make_star(10)
    as.undirected(g)

    # Combining edge attributes
    g3 <- make_ring(10, directed=TRUE, mutual=TRUE)
    E(g3)$weight <- seq_len(ecount(g3))
    ug3 <- as.undirected(g3)
    print(ug3, e=TRUE)
    ## Not run:
      x11(width=10, height=5)
      layout(rbind(1:2))
      plot( g3, layout=layout_in_circle, edge.label=E(g3)$weight)
      plot(ug3, layout=layout_in_circle, edge.label=E(ug3)$weight)

    ## End(Not run)

    g4 <- graph(c(1,2, 3,2,3,4,3,4, 5,4,5,4,
                  6,7, 7,6,7,8,7,8, 8,7,8,9,8,9,
                  9,8,9,8,9,9, 10,10,10,10))
    E(g4)$weight <- seq_len(ecount(g4))
    ug4 <- as.undirected(g4, mode="mutual",
                  edge.attr.comb=list(weight=length))
    print(ug4, e=TRUE)

[Package igraph version 1.2.10 Index]