删除 igraph R 中顶点之间的边

Question

I have an unweighted and undirected graph (A) with 10 vertices and 10 edges.

> A
IGRAPH UNW- 10 10 -- 
+ attr: name (v/c), weight (e/n)

I want to delete a bunch of edges from this graph as defined by vertex pairs, so for example, I want to delete the following edges:

V4 -- V5
V3 -- V7
V3 -- V6

These edges are stored in a data frame called "edges". I want to delete these edges in one go. I tried:

> delete.edges(A,t(edges))

but this does not work and returns the error:

Error in as.igraph.es(graph, edges) : Invalid edge names
In addition: Warning message:
In as.igraph.es(graph, edges) : NAs introduced by coercion

Why does this not work when the equivalent command for adding edges does work?

add.edges(A,t(edges))

How can I delete these edges from graph A in one command? Thanks

Answer 1

Probably the simplest way is to use the graph as an adjacency matrix:

library(igraph)
g <- graph.ring(10)
V(g)$name <- letters[1:10]
str(g)
# IGRAPH UN-- 10 10 -- Ring graph
# + attr: name (g/c), mutual (g/l), circular (g/l), name (v/c)
# + edges (vertex names):
#  [1] a--b b--c c--d d--e e--f f--g g--h h--i i--j a--j


g[ from=c("a","b","c"), to=c("b","c","d") ] <- 0
str(g)
# IGRAPH UN-- 10 7 -- Ring graph
# + attr: name (g/c), mutual (g/l), circular (g/l), name (v/c)
# + edges (vertex names):
# [1] d--e e--f f--g g--h h--i i--j a--j

See more at http://igraph.org/r/doc/graph.structure.html .

Answer 2

The manual suggests to either use E to extract the edges you want to remove from the graph, or edges to construct them from their names (we do not know what your edges data.frame contains).

library(igraph)

# Sample graph
g <- graph.ring(10)
plot(g)

# Edges to remove, as a data.frame
e <- data.frame( 
  from = 1:3,
  to   = 2:4
)

# Convert the data.frame to edges
e <- apply(e, 1, paste, collapse="|")
e <- edges(e)

# Remove the edges and plot the resulting graph.
plot( g - e )

Answer 3

Delete_edges takes a series of edge IDs. Deletion of edges via their incident vertices requires an additional conversion to edge IDs.

ei <- get.edge.ids(g, c(3,6, 3,7, 4,5))

g  <- graph(c(3,6, 3,7, 4,5), 10, directed=FALSE) +
      path(1,2,5,6,7,8,9,10)

ei <- get.edge.ids(g, c(3,6, 3,7, 4,5))
g2 <- delete_edges(g, ei)

Edges can also be removed by symbolic names.

g3 <- set_vertex_attr( g
                     , name="name"
                     , value=strsplit(paste0("V", seq_len(10)), " " )
                     )
g4 <- delete_edges( g3
                  , get.edge.ids(g3, c("V3","V6", "V3","V7", "V4","V5"))
                  )