Create a (small) graph quickly
create_manual_graph(..., simplify = TRUE, graph = c("igraph", "network"))a graph of class network or igraph
This function is useful if you want to create a small (named) graph quickly, it works for both directed and undirected graphs. You need to supply one or more R expressions giving the structure of the graph. The expressions consist of vertex names and edge operators. An edge operator is a sequence of ‘-’ and ‘+’ characters, the former is for the edges and the latter is used for arrow heads. The edges can be arbitrarily long, i.e. you may use as many ‘-’ characters to “draw” them as you like.
This function mainly acts as a wrapper for graph_from_literal
and almost all of the examples come from that function as well.
# undirected graph
create_manual_graph(1-2)
#> IGRAPH c9d2380 UN-- 2 1 --
#> + attr: name (v/c)
#> + edge from c9d2380 (vertex names):
#> [1] 1--2
## the length of the edges does not matter, so the following this creates the same graph
create_manual_graph( 1-----2 )
#> IGRAPH c9d31b0 UN-- 2 1 --
#> + attr: name (v/c)
#> + edge from c9d31b0 (vertex names):
#> [1] 1--2
create_manual_graph(1-2, 1-3, 2-3, 2-4, 3-5, 4-5, 4-6, 4-7, 5-6, 6-7, 8,
graph ="network")
#> Network attributes:
#> vertices = 8
#> directed = FALSE
#> hyper = FALSE
#> loops = FALSE
#> multiple = FALSE
#> bipartite = FALSE
#> total edges= 10
#> missing edges= 0
#> non-missing edges= 10
#>
#> Vertex attribute names:
#> vertex.names
#>
#> No edge attributes
# directed graph
create_manual_graph(Sam-+Mary, Sam-+Tom, Mary++Tom)
#> IGRAPH c9d5713 DN-- 3 4 --
#> + attr: name (v/c)
#> + edges from c9d5713 (vertex names):
#> [1] Sam ->Mary Sam ->Tom Mary->Tom Tom ->Mary
# bipartite graph
g_bipartite <- create_manual_graph(# listing organizations
organization1:organization2:organization3,
# listing projects
project1:project2,
# specifying connections between organizations and projects
organization1:organization2 - project1,
organization2:organization3 - project2)
# note that the graph is bipartite mathematically, but the graph object
# 'does not know' that yet.
snafun::extract_vertex_names(g_bipartite)
#> [1] "organization1" "organization2" "organization3" "project1"
#> [5] "project2"
g_bipartite <- snafun::add_vertex_attributes(g_bipartite, "type",
value = grepl(pattern = "^project", x = snafun::extract_vertex_names(g_bipartite)))
snafun::is_bipartite(g_bipartite)
#> [1] TRUE
# If you have many disconnected components in the graph, separate them with commas.
# You can also give isolate vertices.
create_manual_graph( A--B, C--D, E--F, G--H, I, J, K )
#> IGRAPH c9d7ce1 UN-- 11 4 --
#> + attr: name (v/c)
#> + edges from c9d7ce1 (vertex names):
#> [1] A--B C--D E--F G--H
# The ‘:’ operator can be used to define vertex sets.
# If an edge operator connects two vertex sets then every vertex from the first
# set will be connected to every vertex in the second set.
# The following form creates a full graph, including loop edges:
create_manual_graph( A:B:C:D -- A:B:C:D )
#> IGRAPH c9d8b9e UN-- 4 6 --
#> + attr: name (v/c)
#> + edges from c9d8b9e (vertex names):
#> [1] A--B A--C A--D B--C B--D C--D
# In directed graphs, edges will be created only if the edge operator includes
# a arrow head (‘+’) at the end of the edge:
create_manual_graph( A -+ B -+ C )
#> IGRAPH c9d982d DN-- 3 2 --
#> + attr: name (v/c)
#> + edges from c9d982d (vertex names):
#> [1] A->B B->C
create_manual_graph( A +- B -+ C )
#> IGRAPH c9da507 DN-- 3 2 --
#> + attr: name (v/c)
#> + edges from c9da507 (vertex names):
#> [1] B->A B->C
create_manual_graph( A +- B -- C )
#> IGRAPH c9db2b9 DN-- 3 1 --
#> + attr: name (v/c)
#> + edge from c9db2b9 (vertex names):
#> [1] B->A
# Thus in the third example no edge is created between vertices B and C.
# Mutual edges can be also created with a simple edge operator:
create_manual_graph( A +-+ B +---+ C ++ D + E)
#> IGRAPH c9dbf68 DN-- 5 8 --
#> + attr: name (v/c)
#> + edges from c9dbf68 (vertex names):
#> [1] A->B B->A B->C C->B C->D D->C D->E E->D
# Note again that the length of the edge operators is arbitrary.
# If the vertex names include spaces or other special characters then you
# need to quote them:
create_manual_graph( "this is" +- "a silly" -+ "graph here" )
#> IGRAPH c9dcd27 DN-- 3 2 --
#> + attr: name (v/c)
#> + edges from c9dcd27 (vertex names):
#> [1] a silly->this is a silly->graph here
# You can include any character in the vertex names this way,
# even ‘+’ and ‘-’ characters.
# More examples
# A simple undirected graph
g <- create_manual_graph(
Alice - Bob - Cecil - Alice,
Daniel - Cecil - Eugene,
Cecil - Gordon
)
g
#> IGRAPH c9ddb4d UN-- 6 6 --
#> + attr: name (v/c)
#> + edges from c9ddb4d (vertex names):
#> [1] Alice--Bob Alice--Cecil Bob --Cecil Cecil--Daniel Cecil--Eugene
#> [6] Cecil--Gordon
# Another undirected graph, ":" notation
g2 <- create_manual_graph(Alice - Bob:Cecil:Daniel, Cecil:Daniel - Eugene:Gordon)
g2
#> IGRAPH c9dea39 UN-- 6 7 --
#> + attr: name (v/c)
#> + edges from c9dea39 (vertex names):
#> [1] Alice --Bob Alice --Cecil Alice --Daniel Cecil --Eugene Cecil --Gordon
#> [6] Daniel--Eugene Daniel--Gordon
# A directed graph
g3 <- create_manual_graph(
Alice +-+ Bob --+ Cecil +-- Daniel,
Eugene --+ Gordon:Helen
)
g3
#> IGRAPH c9dfab3 DN-- 7 6 --
#> + attr: name (v/c)
#> + edges from c9dfab3 (vertex names):
#> [1] Alice ->Bob Bob ->Alice Bob ->Cecil Daniel->Cecil Eugene->Gordon
#> [6] Eugene->Helen
# A graph with isolate vertices
g4 <- create_manual_graph(Alice -- Bob -- Daniel, Cecil:Gordon, Helen)
g4
#> IGRAPH c9e0bb9 UN-- 6 2 --
#> + attr: name (v/c)
#> + edges from c9e0bb9 (vertex names):
#> [1] Alice--Bob Bob --Daniel
snafun::extract_vertex_names(g4)
#> [1] "Alice" "Bob" "Daniel" "Cecil" "Gordon" "Helen"
# "Arrows" can be arbitrarily long
g5 <- create_manual_graph(Alice +---------+ Bob)
g5
#> IGRAPH c9e23fd DN-- 2 2 --
#> + attr: name (v/c)
#> + edges from c9e23fd (vertex names):
#> [1] Alice->Bob Bob ->Alice
# Special vertex names
g6 <- create_manual_graph("+" -- "-", "*" -- "/", "%%" -- "%/%")
g6
#> IGRAPH c9e3770 UN-- 6 3 --
#> + attr: name (v/c)
#> + edges from c9e3770 (vertex names):
#> [1] + --- * --/ %%--%/%