Edge sequences can be indexed very much like a plain numeric R vector, with some extras.
## S3 method for class 'igraph.es' x[...]
An edge sequence
Indices, see details below.
Another edge sequence, referring to the same graph.
When using multiple indices within the bracket, all of them
are evaluated independently, and then the results are concatenated
c() function. E.g.
E(g)[1, 2, .inc(1)]
is equivalent to
c(E(g), E(g), E(g)[.inc(1)]).
Edge sequences can be indexed with positive numeric vectors, negative numeric vectors, logical vectors, character vectors:
When indexed with positive numeric vectors, the edges at the given positions in the sequence are selected. This is the same as indexing a regular R atomic vector with positive numeric vectors.
When indexed with negative numeric vectors, the edges at the given positions in the sequence are omitted. Again, this is the same as indexing a regular R atomic vector.
When indexed with a logical vector, the lengths of the edge
sequence and the index must match, and the edges for which the
TRUE are selected.
Named graphs can be indexed with character vectors,
to select edges with the given names. Note that a graph may
have edge names and vertex names, and both can be used to select
edges. Edge names are simply used as names of the numeric
edge id vector. Vertex names effectively only work in graphs without
multiple edges, and must be separated with a
| bar character
to select an edges that incident to the two given vertices. See
When indexing edge sequences, edge attributes can be refered
to simply by using their names. E.g. if a graph has a
E(G)[weight > 1] selects all edges with a larger
than one weight. See more examples below.
There are some special igraph functions that can be used only in expressions indexing edge sequences:
takes a vertex sequence, and selects all edges that have at least one incident vertex in the vertex sequence.
.inc(), but only
the tails of the edges are considered.
is similar to
.inc(), but only
the heads of the edges are considered.
a special operator that can be used to select all edges between two sets of vertices. It ignores the edge directions in directed graphs.
but edges from the left hand side argument, pointing
to the right hand side argument, are selected, in directed
but edges to the left hand side argument, pointing
from the right hand side argument, are selected, in directed
Note that multiple special functions can be used together, or with regular indices, and then their results are concatenated. See more examples below.
Other vertex and edge sequence operations:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
# special operators for indexing based on graph structure g <- sample_pa(100, power = 0.3) E(g) [ 1:3 %--% 2:6 ] E(g) [ 1:5 %->% 1:6 ] E(g) [ 1:3 %<-% 2:6 ] # the edges along the diameter g <- sample_pa(100, directed = FALSE) d <- get_diameter(g) E(g, path = d) # select edges based on attributes g <- sample_gnp(20, 3/20) %>% set_edge_attr("weight", value = rnorm(gsize(.))) E(g)[[ weight < 0 ]]
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