Everything about vertices and vertex selectors also applies to edges and edge selectors unless explicitly noted otherwise.
The vertex (and edge) selector notion was introduced in igraph 0.2. It is a way to reference a sequence of vertices or edges independently of the graph.
While this might sound quite mysterious, it is actually very
simple. For example, all vertices of a graph can be selected by
igraph_vs_all() and the graph independence means that
igraph_vs_all() is not parametrized by a graph object. That is,
igraph_vs_all() is the general concept of selecting all vertices
of a graph. A vertex selector is then a way to specify the class of vertices
to be visited. The selector might specify that all vertices of a graph or
all the neighbours of a vertex are to be visited. A vertex selector is a
way of saying that you want to visit a bunch of vertices, as opposed to a
vertex iterator which is a concrete plan for visiting each of the
chosen vertices of a specific graph.
To determine the actual vertex IDs implied by a vertex selector, you need to apply the concept of selecting vertices to a specific graph object. This can be accomplished by instantiating a vertex iterator using a specific vertex selection concept and a specific graph object. The notion of vertex iterators can be thought of in the following way. Given a specific graph object and the class of vertices to be visited, a vertex iterator is a road map, plan or route for how to visit the chosen vertices.
Some vertex selectors have immediate versions. These have the
prefix igraph_vss instead of igraph_vs, e.g. igraph_vss_all()
instead of igraph_vs_all(). The immediate versions are to be used in
the parameter list of the igraph functions, such as igraph_degree().
These functions are not associated with any igraph_vs_t object, so
they have no separate constructors and destructors
(destroy functions).
igraph_vs_all — Vertex set, all vertices of a graph.igraph_vs_adj — Adjacent vertices of a vertex.igraph_vs_nonadj — Non-adjacent vertices of a vertex.igraph_vs_none — Empty vertex set.igraph_vs_1 — Vertex set with a single vertex.igraph_vs_vector — Vertex set based on a vector.igraph_vs_vector_small — Create a vertex set by giving its elements.igraph_vs_vector_copy — Vertex set based on a vector, with copying.igraph_vs_seq — Vertex set, an interval of vertices.Vertex selectors are created by vertex selector constructors,
can be instantiated with igraph_vit_create(), and are
destroyed with igraph_vs_destroy().
int igraph_vs_all(igraph_vs_t *vs);
Arguments:
|
Pointer to an uninitialized igraph_vs_t object. |
Returns:
Error code. |
See also:
This selector includes all vertices of a given graph in increasing vertex id order.
Time complexity: O(1).
int igraph_vs_adj(igraph_vs_t *vs,
igraph_integer_t vid, igraph_neimode_t mode);
All neighboring vertices of a given vertex are selected by this
selector. The mode argument controls the type of the neighboring
vertices to be selected. The vertices are visited in increasing vertex
ID order, as of igraph version 0.4.
Arguments:
|
Pointer to an uninitialized vertex selector object. |
||||||
|
Vertex ID, the center of the neighborhood. |
||||||
|
Decides the type of the neighborhood for directed graphs. This parameter is ignored for undirected graphs. Possible values:
|
Returns:
Error code. |
See also:
Time complexity: O(1).
int igraph_vs_nonadj(igraph_vs_t *vs, igraph_integer_t vid,
igraph_neimode_t mode);
All non-neighboring vertices of a given vertex. The mode
argument controls the type of neighboring vertices not to
select. Instead of selecting immediate neighbors of vid as is done by
igraph_vs_adj(), the current function selects vertices that are not
immediate neighbors of vid.
Arguments:
|
Pointer to an uninitialized vertex selector object. |
||||||
|
Vertex ID, the “center” of the non-neighborhood. |
||||||
|
The type of neighborhood not to select in directed graphs. Possible values:
|
Returns:
Error code. |
See also:
Time complexity: O(1).
Example 11.1. File examples/simple/igraph_vs_nonadj.c
/* -*- mode: C -*- */ /* IGraph library. Copyright (C) 2006-2012 Gabor Csardi <csardi.gabor@gmail.com> 334 Harvard st, Cambridge MA, 02139 USA This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include <igraph.h> int main () { igraph_t g; igraph_vs_t vs; igraph_vit_t vit; igraph_integer_t size; /* empty graph, all vertices */ igraph_empty(&g, 10, IGRAPH_DIRECTED); igraph_vs_nonadj(&vs, 0, IGRAPH_ALL); igraph_vs_size(&g, &vs, &size); printf("%li ", (long int) size); igraph_vit_create(&g, vs, &vit); while (!IGRAPH_VIT_END(vit)) { printf("%li ", (long int) IGRAPH_VIT_GET(vit)); IGRAPH_VIT_NEXT(vit); } printf("\n"); igraph_vit_destroy(&vit); igraph_vs_destroy(&vs); igraph_destroy(&g); /* full graph, no vertices */ igraph_full(&g, 10, IGRAPH_UNDIRECTED, IGRAPH_LOOPS); igraph_vs_nonadj(&vs, 0, IGRAPH_ALL); igraph_vit_create(&g, vs, &vit); while (!IGRAPH_VIT_END(vit)) { printf("%li ", (long int) IGRAPH_VIT_GET(vit)); IGRAPH_VIT_NEXT(vit); } printf("\n"); igraph_vit_destroy(&vit); igraph_vs_destroy(&vs); igraph_destroy(&g); return 0; }
int igraph_vs_none(igraph_vs_t *vs);
Creates an empty vertex selector.
Arguments:
|
Pointer to an uninitialized vertex selector object. |
Returns:
Error code. |
See also:
Time complexity: O(1).
int igraph_vs_1(igraph_vs_t *vs, igraph_integer_t vid);
This vertex selector selects a single vertex.
Arguments:
|
Pointer to an uninitialized vertex selector object. |
|
The vertex id to be selected. |
Returns:
Error Code. |
See also:
Time complexity: O(1).
int igraph_vs_vector(igraph_vs_t *vs,
const igraph_vector_t *v);
This function makes it possible to handle a vector_t temporarily as a vertex selector. The vertex selector should be thought of like a view to the vector. If you make changes to the vector that also affects the vertex selector. Destroying the vertex selector does not destroy the vector. (Of course.) Do not destroy the vector before destroying the vertex selector, or you might get strange behavior.
Arguments:
|
Pointer to an uninitialized vertex selector. |
|
Pointer to a igraph_vector_t object. |
Returns:
Error code. |
See also:
Time complexity: O(1).
Example 11.2. File examples/simple/igraph_vs_vector.c
/* -*- mode: C -*- */ /* IGraph library. Copyright (C) 2006-2012 Gabor Csardi <csardi.gabor@gmail.com> 334 Harvard st, Cambridge MA, 02139 USA This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include <igraph.h> int main() { igraph_t g; igraph_vector_t v = IGRAPH_VECTOR_NULL; igraph_real_t edges[] = { 0, 1, 1, 2, 2, 2, 2, 3, 2, 4, 3, 4 }; igraph_vector_t v2; long int i; igraph_vit_t vit; igraph_vs_t vs; igraph_integer_t size; igraph_vector_view(&v, edges, sizeof(edges) / sizeof(igraph_real_t)); igraph_create(&g, &v, 0, IGRAPH_DIRECTED); /* Create iterator based on a vector (view) */ igraph_vector_init(&v2, 6); VECTOR(v2)[0] = 0; VECTOR(v2)[1] = 2; VECTOR(v2)[2] = 4; VECTOR(v2)[3] = 0; VECTOR(v2)[4] = 2; VECTOR(v2)[5] = 4; igraph_vit_create(&g, igraph_vss_vector(&v2), &vit); i = 0; while (!IGRAPH_VIT_END(vit)) { if (IGRAPH_VIT_GET(vit) != VECTOR(v2)[i]) { return 1; } IGRAPH_VIT_NEXT(vit); i++; } if (i != igraph_vector_size(&v2)) { return 2; } igraph_vit_destroy(&vit); igraph_vector_destroy(&v2); /* Create small vector iterator */ igraph_vs_vector_small(&vs, 0, 2, 4, 0, 2, 4, 2, -1); igraph_vit_create(&g, vs, &vit); igraph_vs_size(&g, &vs, &size); printf("%li ", (long int) size); for (; !IGRAPH_VIT_END(vit); IGRAPH_VIT_NEXT(vit)) { printf("%li ", (long int) IGRAPH_VIT_GET(vit)); } printf("\n"); igraph_vit_destroy(&vit); igraph_vs_destroy(&vs); /* Clean up */ igraph_destroy(&g); return 0; }
int igraph_vs_vector_small(igraph_vs_t *vs, ...);
This function can be used to create a vertex selector with a couple
of vertices. Do not forget to include a -1 after the
last vertex id. The behavior of the function is undefined if you
don't use a -1 properly.
Note that the vertex ids supplied will be parsed as
int's so you cannot supply arbitrarily large (too
large for int) vertex ids here.
Arguments:
|
Pointer to an uninitialized vertex selector object. |
|
Additional parameters, these will be the vertex ids to
be included in the vertex selector. Supply a |
Returns:
Error code. |
See also:
Time complexity: O(n), the number of vertex ids supplied.
int igraph_vs_vector_copy(igraph_vs_t *vs,
const igraph_vector_t *v);
This function makes it possible to handle a vector_t permanently as a vertex selector. The vertex selector creates a copy of the original vector, so the vector can safely be destroyed after creating the vertex selector. Changing the original vector will not affect the vertex selector. The vertex selector is responsible for deleting the copy made by itself.
Arguments:
|
Pointer to an uninitialized vertex selector. |
|
Pointer to a igraph_vector_t object. |
Returns:
Error code. |
See also:
Time complexity: O(1).
int igraph_vs_seq(igraph_vs_t *vs,
igraph_integer_t from, igraph_integer_t to);
Creates a vertex selector containing all vertices with vertex id
equal to or bigger than from and equal to or smaller than to.
Arguments:
|
Pointer to an uninitialized vertex selector object. |
|
The first vertex id to be included in the vertex selector. |
|
The last vertex id to be included in the vertex selector. |
Returns:
Error code. |
See also:
Time complexity: O(1).
Example 11.3. File examples/simple/igraph_vs_seq.c
/* -*- mode: C -*- */ /* IGraph library. Copyright (C) 2007-2012 Gabor Csardi <csardi.gabor@gmail.com> 334 Harvard st, Cambridge MA, 02139 USA This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include <igraph.h> int main() { igraph_vs_t vs; igraph_vit_t vit; igraph_t g; igraph_integer_t size; igraph_ring(&g, 10, IGRAPH_UNDIRECTED, 0, 1); igraph_vs_seq(&vs, 0, 9); igraph_vit_create(&g, vs, &vit); igraph_vs_size(&g, &vs, &size); printf("%li", (long int) size); while (!IGRAPH_VIT_END(vit)) { printf(" %li", (long int)IGRAPH_VIT_GET(vit)); IGRAPH_VIT_NEXT(vit); } printf("\n"); igraph_vit_destroy(&vit); igraph_vs_destroy(&vs); igraph_destroy(&g); return 0; }
int igraph_vs_copy(igraph_vs_t* dest, const igraph_vs_t* src);
Arguments:
|
The selector being copied. |
|
An uninitialized selector that will contain the copy. |
void igraph_vs_destroy(igraph_vs_t *vs);
This function should be called for all vertex selectors when they
are not needed. The memory allocated for the vertex selector will
be deallocated. Do not call this function on vertex selectors
created with the immediate versions of the vertex selector
constructors (starting with igraph_vss).
Arguments:
|
Pointer to a vertex selector object. |
Time complexity: operating system dependent, usually O(1).
igraph_bool_t igraph_vs_is_all(const igraph_vs_t *vs);
This function checks whether the vertex selector object was created
by igraph_vs_all() or igraph_vss_all(). Note that the
vertex selector might contain all vertices in a given graph but if
it wasn't created by the two constructors mentioned here the return
value will be FALSE.
Arguments:
|
Pointer to a vertex selector object. |
Returns:
TRUE (1) if the vertex selector contains all vertices and FALSE (0) otherwise. |
Time complexity: O(1).
igraph_vss_all — All vertices of a graph (immediate version).igraph_vss_none — Empty vertex set (immediate version).igraph_vss_1 — Vertex set with a single vertex (immediate version).igraph_vss_vector — Vertex set based on a vector (immediate version).igraph_vss_seq — An interval of vertices (immediate version).
igraph_vs_t igraph_vss_all(void);
Immediate vertex selector for all vertices in a graph. It can be used conveniently when some vertex property (e.g. betweenness, degree, etc.) should be calculated for all vertices.
Returns:
A vertex selector for all vertices in a graph. |
See also:
Time complexity: O(1).
igraph_vs_t igraph_vss_none(void);
The immediate version of the empty vertex selector.
Returns:
An empty vertex selector. |
See also:
Time complexity: O(1).
igraph_vs_t igraph_vss_1(igraph_integer_t vid);
The immediate version of the single-vertex selector.
Arguments:
|
The vertex to be selected. |
Returns:
A vertex selector containing a single vertex. |
See also:
Time complexity: O(1).
igraph_vs_t igraph_vss_vector(const igraph_vector_t *v);
This is the immediate version of igraph_vs_vector.
Arguments:
|
Pointer to a igraph_vector_t object. |
Returns:
A vertex selector object containing the vertices in the vector. |
See also:
Time complexity: O(1).
igraph_vs_t igraph_vss_seq(igraph_integer_t from, igraph_integer_t to);
The immediate version of igraph_vs_seq().
Arguments:
|
The first vertex id to be included in the vertex selector. |
|
The last vertex id to be included in the vertex selector. |
Returns:
Error code. |
See also:
Time complexity: O(1).
igraph_vit_create — Creates a vertex iterator from a vertex selector.igraph_vit_destroy — Destroys a vertex iterator.IGRAPH_VIT_NEXT — Next vertex.IGRAPH_VIT_END — Are we at the end?IGRAPH_VIT_SIZE — Size of a vertex iterator.IGRAPH_VIT_RESET — Reset a vertex iterator.IGRAPH_VIT_GET — Query the current position.
int igraph_vit_create(const igraph_t *graph,
igraph_vs_t vs, igraph_vit_t *vit);
This function instantiates a vertex selector object with a given
graph. This is the step when the actual vertex ids are created from
the logical notion of the vertex selector based on the graph.
E.g. a vertex selector created with igraph_vs_all() contains
knowledge that all vertices are included in a (yet indefinite)
graph. When instantiating it a vertex iterator object is created,
this contains the actual vertex ids in the graph supplied as a
parameter.
The same vertex selector object can be used to instantiate any number vertex iterators.
Arguments:
|
An igraph_t object, a graph. |
|
A vertex selector object. |
|
Pointer to an uninitialized vertex iterator object. |
Returns:
Error code. |
See also:
Time complexity: it depends on the vertex selector type. O(1) for
vertex selectors created with igraph_vs_all(), igraph_vs_none(), igraph_vs_1, igraph_vs_vector, igraph_vs_seq(), igraph_vs_vector(), igraph_vs_vector_small(). O(d) for igraph_vs_adj(), d is the
number of vertex ids to be included in the iterator. O(|V|) for
igraph_vs_nonadj(), |V| is the number of vertices in the graph.
void igraph_vit_destroy(const igraph_vit_t *vit);
Deallocates memory allocated for a vertex iterator.
Arguments:
|
Pointer to an initialized vertex iterator object. |
See also:
Time complexity: operating system dependent, usually O(1).
After creating an iterator with igraph_vit_create(), it
points to the first vertex in the vertex determined by the vertex
selector (if there is any). The IGRAPH_VIT_NEXT() macro steps
to the next vertex, IGRAPH_VIT_END() checks whether there are
more vertices to visit, IGRAPH_VIT_SIZE() gives the total size
of the vertices visited so far and to be visited. IGRAPH_VIT_RESET() resets the iterator, it will point to the first
vertex again. Finally IGRAPH_VIT_GET() gives the current vertex
pointed to by the iterator (call this only if IGRAPH_VIT_END()
is false).
Here is an example on how to step over the neighbors of vertex 0:
igraph_vs_t vs;
igraph_vit_t vit;
...
igraph_vs_adj(&vs, 0, IGRAPH_ALL);
igraph_vit_create(&graph, vs, &vit);
while (!IGRAPH_VIT_END(vit)) {
printf(" %li", (long int) IGRAPH_VIT_GET(vit));
IGRAPH_VIT_NEXT(vit);
}
printf("\n");
...
igraph_vit_destroy(&vit);
igraph_vs_destroy(&vs);
#define IGRAPH_VIT_NEXT(vit)
Steps the iterator to the next vertex. Only call this function if
IGRAPH_VIT_END() returns false.
Arguments:
|
The vertex iterator to step. |
Time complexity: O(1).
#define IGRAPH_VIT_END(vit)
Checks whether there are more vertices to step to.
Arguments:
|
The vertex iterator to check. |
Returns:
Logical value, if true there are no more vertices to step to. |
Time complexity: O(1).
#define IGRAPH_VIT_SIZE(vit)
Gives the number of vertices in a vertex iterator.
Arguments:
|
The vertex iterator. |
Returns:
The number of vertices. |
Time complexity: O(1).
igraph_es_all — Edge set, all edges.igraph_es_incident — Edges incident on a given vertex.igraph_es_none — Empty edge selector.igraph_es_1 — Edge selector containing a single edge.igraph_es_vector — Handle a vector as an edge selector.igraph_es_fromto — Edge selector, all edges between two vertex sets.igraph_es_seq — Edge selector, a sequence of edge ids.igraph_es_pairs — Edge selector, multiple edges defined by their endpoints in a vector.igraph_es_pairs_small — Edge selector, multiple edges defined by their endpoints as arguments.igraph_es_path — Edge selector, edge ids on a path.igraph_es_vector_copy — Edge set, based on a vector, with copying.
int igraph_es_all(igraph_es_t *es,
igraph_edgeorder_type_t order);
Arguments:
|
Pointer to an uninitialized edge selector object. |
|
Constant giving the order in which the edges will be
included in the selector. Possible values:
|
Returns:
Error code. |
See also:
Time complexity: O(1).
int igraph_es_incident(igraph_es_t *es,
igraph_integer_t vid, igraph_neimode_t mode);
Arguments:
|
Pointer to an uninitialized edge selector object. |
|
Vertex id, of which the incident edges will be selected. |
|
Constant giving the type of the incident edges to
select. This is ignored for undirected graphs. Possible values:
|
Returns:
Error code. |
See also:
Time complexity: O(1).
int igraph_es_none(igraph_es_t *es);
Arguments:
|
Pointer to an uninitialized edge selector object to initialize. |
Returns:
Error code. |
See also:
Time complexity: O(1).
int igraph_es_1(igraph_es_t *es, igraph_integer_t eid);
Arguments:
|
Pointer to an uninitialized edge selector object. |
|
Edge id of the edge to select. |
Returns:
Error code. |
See also:
Time complexity: O(1).
int igraph_es_vector(igraph_es_t *es,
const igraph_vector_t *v);
Creates an edge selector which serves as a view to a vector containing edge ids. Do not destroy the vector before destroying the view. Many views can be created to the same vector.
Arguments:
|
Pointer to an uninitialized edge selector. |
|
Vector containing edge ids. |
Returns:
Error code. |
See also:
Time complexity: O(1).
int igraph_es_fromto(igraph_es_t *es,
igraph_vs_t from, igraph_vs_t to);
This function is not implemented yet.
Arguments:
|
Pointer to an uninitialized edge selector. |
|
Vertex selector, their outgoing edges will be selected. |
|
Vertex selector, their incoming edges will be selected from the previous selection. |
Returns:
Error code. |
See also:
Time complexity: O(1).
int igraph_es_seq(igraph_es_t *es,
igraph_integer_t from, igraph_integer_t to);
All edge ids between from and to will be
included in the edge selection. This includes from and
excludes to.
Arguments:
|
Pointer to an uninitialized edge selector object. |
|
The first edge id to be included. |
|
The last edge id to be included. |
Returns:
Error code. |
See also:
Time complexity: O(1).
int igraph_es_pairs(igraph_es_t *es, const igraph_vector_t *v,
igraph_bool_t directed);
The edges between the given pairs of vertices will be included in the
edge selection. The vertex pairs must be defined in the vector v,
the first element of the vector is the first vertex of the first edge
to be selected, the second element is the second vertex of the first
edge, the third element is the first vertex of the second edge and
so on.
Arguments:
|
Pointer to an uninitialized edge selector object. |
|
The vector containing the endpoints of the edges. |
|
Whether the graph is directed or not. |
Returns:
Error code. |
See also:
Time complexity: O(n), the number of edges being selected.
Example 11.4. File examples/simple/igraph_es_pairs.c
/* -*- mode: C -*- */ /* IGraph library. Copyright (C) 2006-2012 Gabor Csardi <csardi.gabor@gmail.com> 334 Harvard st, Cambridge MA, 02139 USA This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include <igraph.h> int main() { igraph_t g; long int i; igraph_integer_t size; /* DIRECTED */ igraph_star(&g, 10, IGRAPH_STAR_OUT, 0); for (i = 0; i < 100; i++) { igraph_es_t es; igraph_eit_t it; igraph_es_pairs_small(&es, IGRAPH_DIRECTED, 0, 1, 0, 2, 0, 5, 0, 2, 0, 3, 0, 4, 0, 7, 0, 9, -1); igraph_eit_create(&g, es, &it); igraph_es_size(&g, &es, &size); IGRAPH_EIT_RESET(it); while (!IGRAPH_EIT_END(it)) { (void) IGRAPH_EIT_GET(it); IGRAPH_EIT_NEXT(it); size--; } if (size != 0) { return 1; } igraph_eit_destroy(&it); igraph_es_destroy(&es); } igraph_destroy(&g); /* UNDIRECTED */ igraph_star(&g, 10, IGRAPH_STAR_UNDIRECTED, 0); for (i = 0; i < 100; i++) { igraph_es_t es; igraph_eit_t it; igraph_es_pairs_small(&es, IGRAPH_DIRECTED, 0, 1, 2, 0, 5, 0, 0, 2, 3, 0, 0, 4, 7, 0, 0, 9, -1); igraph_eit_create(&g, es, &it); IGRAPH_EIT_RESET(it); while (!IGRAPH_EIT_END(it)) { (void) IGRAPH_EIT_GET(it); IGRAPH_EIT_NEXT(it); } igraph_eit_destroy(&it); igraph_es_destroy(&es); } igraph_destroy(&g); return 0; }
int igraph_es_pairs_small(igraph_es_t *es, igraph_bool_t directed, ...);
The edges between the given pairs of vertices will be included in the edge selection. The vertex pairs must be given as the arguments of the function call, the third argument is the first vertex of the first edge, the fourth argument is the second vertex of the first edge, the fifth is the first vertex of the second edge and so on. The last element of the argument list must be -1 to denote the end of the argument list.
Arguments:
|
Pointer to an uninitialized edge selector object. |
|
Whether the graph is directed or not. |
Returns:
Error code. |
See also:
Time complexity: O(n), the number of edges being selected.
int igraph_es_path(igraph_es_t *es, const igraph_vector_t *v,
igraph_bool_t directed);
This function takes a vector of vertices and creates a selector of edges between those vertices. Vector {0, 3, 4, 7} will select edges (0 -> 3), (3 -> 4), (4 -> 7). If these edges don't exist then trying to create an iterator using this selector will fail.
Arguments:
|
Pointer to an uninitialized edge selector object. |
|
Pointer to a vector of vertex id's along the path. |
|
If edge directions should be taken into account. This will be ignored if the graph to select from is undirected. |
Returns:
Error code. |
See also:
Time complexity: O(n), the number of vertices.
int igraph_es_vector_copy(igraph_es_t *es, const igraph_vector_t *v);
This function makes it possible to handle a vector_t permanently as an edge selector. The edge selector creates a copy of the original vector, so the vector can safely be destroyed after creating the edge selector. Changing the original vector will not affect the edge selector. The edge selector is responsible for deleting the copy made by itself.
Arguments:
|
Pointer to an uninitialized edge selector. |
|
Pointer to a igraph_vector_t object. |
Returns:
Error code. |
See also:
Time complexity: O(1).
igraph_ess_all — Edge set, all edges (immediate version)igraph_ess_none — Immediate empty edge selector.igraph_ess_1 — Immediate version of the single edge edge selector.igraph_ess_vector — Immediate vector view edge selector.igraph_ess_seq — Immediate version of the sequence edge selector.
igraph_es_t igraph_ess_all(igraph_edgeorder_type_t order);
The immediate version of the all-edges selector.
Arguments:
|
Constant giving the order of the edges in the edge
selector. See |
Returns:
The edge selector. |
See also:
Time complexity: O(1).
igraph_es_t igraph_ess_none(void);
Immediate version of the empty edge selector.
Returns:
Initialized empty edge selector. |
See also:
Time complexity: O(1).
igraph_es_t igraph_ess_1(igraph_integer_t eid);
Arguments:
|
The id of the edge. |
Returns:
The edge selector. |
See also:
Time complexity: O(1).
igraph_es_t igraph_ess_vector(const igraph_vector_t *v);
This is the immediate version of the vector of edge ids edge selector.
Arguments:
|
The vector of edge ids. |
Returns:
Edge selector, initialized. |
See also:
Time complexity: O(1).
igraph_es_as_vector — Transform edge selector into vector.igraph_es_copy — Creates a copy of an edge selector.igraph_es_destroy — Destroys an edge selector object.igraph_es_is_all — Check whether an edge selector includes all edges.igraph_es_size — Returns the size of the edge selector.igraph_es_type — Returns the type of the edge selector.
int igraph_es_as_vector(const igraph_t *graph, igraph_es_t es,
igraph_vector_t *v);
Call this function on an edge selector to transform it into a vector. This is only implemented for sequence and vector selectors. If the edges do not exist in the graph, this will result in an error.
Arguments:
|
Pointer to a graph to check if the edges in the selector exist. |
|
An edge selector object. |
|
Pointer to initialized vector. The result will be stored here. |
Time complexity: O(n), the number of edges in the selector.
int igraph_es_copy(igraph_es_t* dest, const igraph_es_t* src);
Arguments:
|
The selector being copied. |
|
An uninitialized selector that will contain the copy. |
See also:
void igraph_es_destroy(igraph_es_t *es);
Call this function on an edge selector when it is not needed any more. Do not call this function on edge selectors created by immediate constructors, those don't need to be destroyed.
Arguments:
|
Pointer to an edge selector object. |
Time complexity: operating system dependent, usually O(1).
igraph_bool_t igraph_es_is_all(const igraph_es_t *es);
Arguments:
|
Pointer to an edge selector object. |
Returns:
TRUE (1) if |
Time complexity: O(1).
igraph_eit_create — Creates an edge iterator from an edge selector.igraph_eit_destroy — Destroys an edge iterator.IGRAPH_EIT_NEXT — Next edge.IGRAPH_EIT_END — Are we at the end?IGRAPH_EIT_SIZE — Number of edges in the iterator.IGRAPH_EIT_RESET — Reset an edge iterator.IGRAPH_EIT_GET — Query an edge iterator.
int igraph_eit_create(const igraph_t *graph,
igraph_es_t es, igraph_eit_t *eit);
This function creates an edge iterator based on an edge selector and a graph.
The same edge selector can be used to create many edge iterators, also for different graphs.
Arguments:
|
An igraph_t object for which the edge selector will be instantiated. |
|
The edge selector to instantiate. |
|
Pointer to an uninitialized edge iterator. |
Returns:
Error code. |
See also:
Time complexity: depends on the type of the edge selector. For edge
selectors created by igraph_es_all(), igraph_es_none(),
igraph_es_1(), igraph_es_vector(), igraph_es_seq() it is
O(1). For igraph_es_incident() it is O(d) where d is the number of
incident edges of the vertex.
void igraph_eit_destroy(const igraph_eit_t *eit);
Arguments:
|
Pointer to an edge iterator to destroy. |
See also:
Time complexity: operating system dependent, usually O(1).
Just like for vertex iterators, macros are provided for
stepping over a sequence of edges: IGRAPH_EIT_NEXT() goes to
the next edge, IGRAPH_EIT_END() checks whether there are more
edges to visit, IGRAPH_EIT_SIZE() gives the number of edges in
the edge sequence, IGRAPH_EIT_RESET() resets the iterator to
the first edge and IGRAPH_EIT_GET() returns the id of the
current edge.
#define IGRAPH_EIT_NEXT(eit)
Steps the iterator to the next edge. Call this function only if
IGRAPH_EIT_END() returns false.
Arguments:
|
The edge iterator to step. |
Time complexity: O(1).
#define IGRAPH_EIT_END(eit)
Checks whether there are more edges to step to.
Arguments:
|
The edge iterator to check. |
Returns:
Logical value, if true there are no more edges to step to. |
Time complexity: O(1).
#define IGRAPH_EIT_SIZE(eit)
Gives the number of edges in an edge iterator.
Arguments:
|
The edge iterator. |
Returns:
The number of edges. |
Time complexity: O(1).
| ← Chapter 10. Games on graphs | Chapter 12. Graph, vertex and edge attributes → |