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Union of graphs

Source: R/operators.R
union.igraph.Rd

The union of two or more graphs are created. The graphs may have identical or overlapping vertex sets.

Usage

# S3 method for class 'igraph'
union(
  ...,
  byname = "auto",
  graph.attr.comb = igraph_opt("graph.attr.comb"),
  vertex.attr.comb = "rename",
  edge.attr.comb = "rename"
)

Arguments

...

Graph objects or lists of graph objects.

byname

A Logical, or the character scalar auto. Whether to perform the operation based on symbolic vertex names. If it is auto, that means TRUE if all graphs are named and FALSE otherwise. A warning is generated if auto and some (but not all) graphs are named.

graph.attr.comb, vertex.attr.comb, edge.attr.comb

Specification for combining clashing graph, vertex and edge attributes. vertex.attr.comb and edge.attr.comb default to "rename"; graph.attr.comb defaults to the graph.attr.comb igraph option ("rename" unless changed via igraph_options()). "rename" preserves the historical behaviour of appending _1, _2, ... suffixes. See igraph-attribute-combination for the available combiners.

Value

A new graph object.

Details

union() creates the union of two or more graphs. Edges which are included in at least one graph will be part of the new graph. This function can be also used via the %u% operator.

If the byname argument is TRUE (or auto and all graphs are named), then the operation is performed on symbolic vertex names instead of the internal numeric vertex IDs.

union() keeps the attributes of all graphs. All graph, vertex and edge attributes are copied to the result. By default, if an attribute is present in multiple graphs and would result in a name clash, that attribute is renamed by adding suffixes: _1, _2, etc. Pass graph.attr.comb, vertex.attr.comb or edge.attr.comb to combine clashing attributes instead, e.g. by summing or by taking the first non-NA value. See igraph-attribute-combination for the available combiners.

The name vertex attribute is treated specially if the operation is performed based on symbolic vertex names. In this case name must be present in all graphs, and it is not renamed in the result graph.

An error is generated if some input graphs are directed and others are undirected.

vcount(), permute_vertices(), edges(), get_eids(), ecount()

See also

Other functions for manipulating graph structure: +.igraph(), add_edges(), add_vertices(), complementer(), compose(), connect(), contract(), delete_edges(), delete_vertices(), difference(), difference.igraph(), disjoint_union(), edge(), igraph-minus, intersection(), intersection.igraph(), path(), permute(), rep.igraph(), reverse_edges(), simplify(), transitive_closure(), union(), vertex()

Author

Gabor Csardi csardi.gabor@gmail.com

Examples


## Union of two social networks with overlapping sets of actors
net1 <- graph_from_literal(
  D - A:B:F:G, A - C - F - A, B - E - G - B, A - B, F - G,
  H - F:G, H - I - J
)
net2 <- graph_from_literal(D - A:F:Y, B - A - X - F - H - Z, F - Y)
print_all(net1 %u% net2)
#> ── <igraph> ───────────────────────────────────────────────────────── 595bb76 ──
#> ℹ undirected · named
#> ℹ 13 vertices · 21 edges
#> 
#> ── Attributes ──────────────────────────────────────────────────────────────────
#> → vertex: name <chr>
#> 
#> ── Vertex attributes ───────────────────────────────────────────────────────────
#>      name
#> [1]     D
#> [2]     A
#> [3]     B
#> [4]     F
#> [5]     G
#> [6]     C
#> [7]     E
#> [8]     H
#> [9]     I
#> [10]    J
#> [11]    Y
#> [12]    X
#> [13]    Z
#> 
#> ── Edges (vertex names) ────────────────────────────────────────────────────────
#>  [1] I ─ J  H ─ Z  H ─ I  G ─ H  G ─ E  F ─ X  F ─ Y  F ─ H  F ─ C  F ─ G 
#> [11] B ─ E  B ─ G  A ─ X  A ─ C  A ─ F  A ─ B  D ─ Y  D ─ G  D ─ F  D ─ B 
#> [21] D ─ A