edgeWeights
Retrieve the edge weights of a graph
A generic function that returns the edge weights of a graph. If
index
is specified, only the weights for the edges from the
specified nodes are returned. The user can control which edge
attribute is interpreted as the weight, see the Details section.
 Keywords
 manip
Usage
edgeWeights(object, index, ..., attr = "weight", default = 1, type.checker = is.numeric)
Arguments
 object
 A graph, any object that inherits from the
graph
class.  index
 If supplied, a character or numeric vector of node names or indices.
 ...
 Unused.
 attr
 The name of the edge attribute to use as a weight. You
can view the list of defined edge attributes and their default values
using
edgeDataDefaults
. The default attribute name is"weight"
, see the Details section.  default
 The value to use if
object
has no edge attribute named by the value ofattr
. The default is the value 1 (double).  type.checker
 A function that will be used to check that the
edge weights are of the correct type. This function should return
TRUE if the input vector is of the right type and FALSE otherwise.
The default is to check for numeric edge weights using
is.numeric
. If no type checking is desired, specifyNULL
.
Details
If index
is suppled, then edge weights from these nodes to all
adjacent nodes are returned. If index
is not supplied, then the
edge weights for all nodes are returned. The value for nodes without
any outgoing edges will be a zerolength vector of the appropriate
mode.
The edgeWeights
method is a convenience wrapper around
edgeData
, the generalpurpose way to access edge attribute
information for a graph
instance. In general, edge attributes
can be arbitary R objects. However, for edgeWeights
to make
sense, the values must be vectors of length not more than one.
By default, edgeWeights
looks for an edge attribute with name
"weight"
and, if found, uses these values to construct the edge
weight list. You can make use of attributes stored under a different
name by providing a value for the attr
argument. For example,
if object
is a graph instance with an edge attribute named
"WTS"
, then the call edgeWeights(object, attr="WTS")
will attempt to use those values.
The function specified by type.checker
will be given a vector
of edge weights; if the return value is not TRUE
, then an error
will be signaled indicating that the edge weights in the graph are not
of the expected type. Type checking is skipped if type.checker
is NULL
.
If the graph instance does not have an edge attribute with name given
by the value of the attr
argument, default
will be used
as the weight for all edges. Note that if there is an attribute named
by attr
, then its default value will be used for edges not
specifically customized. See edgeData
and
edgeDataDefaults
for more information.
Because of their position after the ...
, no partial matching is
performed for the arguments attr
, default
, and
type.checker
.
Value

A named list of named edge weight vectors. The names on the list are
the names of the nodes specified by
index
, or all nodes if
index
was not provided. The names on the weight vectors are
node names to identify the edge to which the weight belongs.
See Also
nodes
edges
edgeData
edgeDataDefaults
is.numeric
is.integer
is.character
Examples
V < LETTERS[1:4]
edL2 < vector("list", length=4)
names(edL2) < V
for(i in 1:4)
edL2[[i]] < list(edges=c(2,1,2,1)[i], weights=sqrt(i))
gR2 < graphNEL(nodes=V, edgeL=edL2, edgemode="directed")
edgeWeights(gR2, "C")
edgeWeights(gR2)
edgeWeights(gR2, attr="foo", default=5)
edgeData(gR2, attr="weight")
edgeData(gR2, from="C", attr="weight")