1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
|
% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/make.R
\name{graph_from_literal}
\alias{graph_from_literal}
\alias{from_literal}
\title{Creating (small) graphs via a simple interface}
\usage{
graph_from_literal(..., simplify = TRUE)
from_literal(...)
}
\arguments{
\item{...}{For \code{graph_from_literal()} the formulae giving the
structure of the graph, see details below. For \code{from_literal()}
all arguments are passed to \code{graph_from_literal()}.}
\item{simplify}{Logical scalar, whether to call \code{\link[=simplify]{simplify()}}
on the created graph. By default the graph is simplified, loop and
multiple edges are removed.}
}
\value{
An igraph graph
}
\description{
This function is useful if you want to create a small (named) graph
quickly, it works for both directed and undirected graphs.
}
\details{
\code{graph_from_literal()} is very handy for creating small graphs quickly.
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 \sQuote{\code{-}} and
\sQuote{\code{+}} 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 \sQuote{\code{-}} characters to \dQuote{draw}
them as you like.
If all edge operators consist of only \sQuote{\code{-}} characters
then the graph will be undirected, whereas a single \sQuote{\code{+}}
character implies a directed graph.
Let us see some simple examples. Without arguments the function
creates an empty graph:
\preformatted{ graph_from_literal()
}
A simple undirected graph with two vertices called \sQuote{A} and
\sQuote{B} and one edge only:
\preformatted{ graph_from_literal(A-B)
}
Remember that the length of the edges does not matter, so we could
have written the following, this creates the same graph:
\preformatted{ graph_from_literal( A-----B )
}
If you have many disconnected components in the graph, separate them
with commas. You can also give isolate vertices.
\preformatted{ graph_from_literal( A--B, C--D, E--F, G--H, I, J, K )
}
The \sQuote{\code{:}} 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:
\preformatted{ graph_from_literal( A:B:C:D -- A:B:C:D )
}
In directed graphs, edges will be created only if the edge operator
includes a arrow head (\sQuote{+}) \emph{at the end} of the edge:
\preformatted{ graph_from_literal( A -+ B -+ C )
graph_from_literal( A +- B -+ C )
graph_from_literal( A +- B -- C )
}
Thus in the third example no edge is created between vertices \code{B}
and \code{C}.
Mutual edges can be also created with a simple edge operator:
\preformatted{ graph_from_literal( A +-+ B +---+ C ++ D + E)
}
Note again that the length of the edge operators is arbitrary,
\sQuote{\code{+}}, \sQuote{\verb{++}} and \sQuote{\verb{+-----+}} have
exactly the same meaning.
If the vertex names include spaces or other special characters then
you need to quote them:
\preformatted{ graph_from_literal( "this is" +- "a silly" -+ "graph here" )
}
You can include any character in the vertex names this way, even
\sQuote{+} and \sQuote{-} characters.
See more examples below.
}
\examples{
# A simple undirected graph
g <- graph_from_literal(
Alice - Bob - Cecil - Alice,
Daniel - Cecil - Eugene,
Cecil - Gordon
)
g
# Another undirected graph, ":" notation
g2 <- graph_from_literal(Alice - Bob:Cecil:Daniel, Cecil:Daniel - Eugene:Gordon)
g2
# A directed graph
g3 <- graph_from_literal(
Alice +-+ Bob --+ Cecil +-- Daniel,
Eugene --+ Gordon:Helen
)
g3
# A graph with isolate vertices
g4 <- graph_from_literal(Alice -- Bob -- Daniel, Cecil:Gordon, Helen)
g4
V(g4)$name
# "Arrows" can be arbitrarily long
g5 <- graph_from_literal(Alice +---------+ Bob)
g5
# Special vertex names
g6 <- graph_from_literal("+" -- "-", "*" -- "/", "\%\%" -- "\%/\%")
g6
}
\seealso{
Other deterministic constructors:
\code{\link{graph_from_atlas}()},
\code{\link{graph_from_edgelist}()},
\code{\link{make_}()},
\code{\link{make_chordal_ring}()},
\code{\link{make_empty_graph}()},
\code{\link{make_full_citation_graph}()},
\code{\link{make_full_graph}()},
\code{\link{make_graph}()},
\code{\link{make_lattice}()},
\code{\link{make_ring}()},
\code{\link{make_star}()},
\code{\link{make_tree}()}
}
\concept{deterministic constructors}
|
