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The difference of two graphs are created.


# S3 method for igraph
difference(big, small, byname = "auto", ...)



The left hand side argument of the minus operator. A directed or undirected graph.


The right hand side argument of the minus operator. A directed ot undirected graph.


A logical scalar, or the character scalar auto. Whether to perform the operation based on symbolic vertex names. If it is auto, that means TRUE if both graphs are named and FALSE otherwise. A warning is generated if auto and one graph, but not both graphs are named.


Ignored, included for S3 compatibility.


A new graph object.


difference() creates the difference of two graphs. Only edges present in the first graph but not in the second will be be included in the new graph. The corresponding operator is %m%.

If the byname argument is TRUE (or auto and the graphs are all named), then the operation is performed based on symbolic vertex names. Otherwise numeric vertex ids are used.

difference() keeps all attributes (graph, vertex and edge) of the first graph.

Note that big and small must both be directed or both be undirected, otherwise an error message is given.


Gabor Csardi


## Create a wheel graph
wheel <- union(
  make_star(11, center = 11, mode = "undirected")
V(wheel)$name <- letters[seq_len(vcount(wheel))]

## Subtract a star graph from it
sstar <- make_star(6, center = 6, mode = "undirected")
V(sstar)$name <- letters[c(1, 3, 5, 7, 9, 11)]
G <- wheel %m% sstar
#> IGRAPH 39dcb97 UN-- 11 15 -- 
#> + attr: name_1 (g/c), name_2 (g/c), mutual (g/l), circular (g/l), mode
#> | (g/c), center (g/n), name (v/c)
#> + edges (vertex names):
#> a -- b, j
#> b -- a, c, k
#> c -- b, d
#> d -- c, e, k
#> e -- d, f
#> f -- e, g, k
#> g -- f, h
#> h -- g, i, k
#> i -- h, j
#> j -- a, i, k
#> k -- b, d, f, h, j
plot(G, layout = layout_nicely(wheel))