The ::struct::graph command creates a new graph object with an associated global Tcl command whose name
is graphName. This command may be used to invoke various operations on the graph. It has the following
general form:
graphNameoption ?argarg...?
Option and the args determine the exact behavior of the command.
A directed graph is a structure containing two collections of elements, called nodes and arcs
respectively, together with a relation ("connectivity") that places a general structure upon the nodes
and arcs.
Each arc is connected to two nodes, one of which is called the source and the other the target. This
imposes a direction upon the arc, which is said to go from the source to the target. It is allowed that
source and target of an arc are the same node. Such an arc is called a loop. Whenever a node is source or
target of an arc both are said to be adjacent. This extends into a relation between nodes, i.e. if two
nodes are connected through at least one arc they are said to be adjacent too.
Each node can be the source and target for any number of arcs. The former are called the outgoingarcs of
the node, the latter the incomingarcs of the node. The number of edges in either set is called the in-
resp. the out-degree of the node.
In addition to maintaining the node and arc relationships, this graph implementation allows any number of
keyed values to be associated with each node and arc.
The following commands are possible for graph objects:
graphNamedestroy
Destroy the graph, including its storage space and associated command.
graphNamearcappendarc ?-key key? value
Appends a value to one of the keyed values associated with an arc. If no key is specified, the key
data is assumed.
graphNamearcdeletearc ?arc ...?
Remove the specified arcs from the graph.
graphNamearcexistsarc
Return true if the specified arc exists in the graph.
graphNamearcgetarc ?-key key?
Return the value associated with the key key for the arc. If no key is specified, the key data is
assumed.
graphNamearcgetallarc
Returns a serialized list of key/value pairs (suitable for use with [arrayset]) for the arc.
graphNamearckeysarc
Returns a list of keys for the arc.
graphNamearckeyexistsarc ?-key key?
Return true if the specified key exists for the arc. If no key is specified, the key data is
assumed.
graphNamearcinsertstartend ?child?
Insert an arc named child into the graph beginning at the node start and ending at the node end.
If the name of the new arc is not specified the system will generate a unique name of the form
arcx.
graphNamearclappendarc ?-key key? value
Appends a value (as a list) to one of the keyed values associated with an arc. If no key is
specified, the key data is assumed.
graphNamearcsetarc ?-key key? ?value?
Set or get one of the keyed values associated with an arc. If no key is specified, the key data
is assumed. Each arc that is added to a graph has the empty string assigned to the key data
automatically. An arc may have any number of keyed values associated with it. If value is not
specified, this command returns the current value assigned to the key; if value is specified, this
command assigns that value to the key.
graphNamearcsourcearc
Return the node the given arc begins at.
graphNamearctargetarc
Return the node the given arc ends at.
graphNamearcunsetarc ?-key key?
Remove a keyed value from the arc arc. If no key is specified, the key data is assumed.
graphNamearcs ?-key key? ?-value value? ?-in|-out|-adj|-inner|-embedding nodelist?
Return a list of arcs in the graph. If no restriction is specified a list containing all arcs is
returned. Restrictions can limit the list of returned arcs based on the nodes that are connected
by the arc, on the keyed values associated with the arc, or both. The restrictions that involve
connected nodes have a list of nodes as argument, specified after the name of the restriction
itself.
-in Return a list of all arcs whose target is one of the nodes in the nodelist.
-out Return a list of all arcs whose source is one of the nodes in the nodelist.
-adj Return a list of all arcs adjacent to at least one of the nodes in the nodelist. This is
the union of the nodes returned by -in and -out.
-inner Return a list of all arcs adjacent to two of the nodes in the nodelist. This is the set of
arcs in the subgraph spawned by the specified nodes.
-embedding
Return a list of all arcs adjacent to exactly one of the nodes in the nodelist. This is the
set of arcs connecting the subgraph spawned by the specified nodes to the rest of the
graph.
-keykey
Limit the list of arcs that are returned to those arcs that have an associated key key.
-valuevalue
This restriction can only be used in combination with -key. It limits the list of arcs that
are returned to those arcs whose associated key key has the value value.
The restrictions imposed by either -in, -out, -adj, -inner, or -embedded are applied first. Specifying
more than one of them is illegal. At last the restrictions set via -key (and -value) are applied.
Specifying more than one -key (and -value) is illegal.
graphNamenodeappendnode ?-key key? value
Appends a value to one of the keyed values associated with an node. If no key is specified, the
key data is assumed.
graphNamenodedegree ?-in|-out? node
Return the number of arcs adjacent to the specified node. If one of the restrictions -in or -out
is given only the incoming resp. outgoing arcs are counted.
graphNamenodedeletenode ?node ...?
Remove the specified nodes from the graph. All of the nodes' arcs will be removed as well to
prevent unconnected arcs.
graphNamenodeexistsnode
Return true if the specified node exists in the graph.
graphNamenodegetnode ?-key key?
Return the value associated with the key key for the node. If no key is specified, the key data
is assumed.
graphNamenodegetallnode
Returns a serialized list of key/value pairs (suitable for use with [arrayset]) for the node.
graphNamenodekeysnode
Returns a list of keys for the node.
graphNamenodekeyexistsnode ?-key key?
Return true if the specified key exists for the node. If no key is specified, the key data is
assumed.
graphNamenodeinsert ?child?
Insert a node named child into the graph. The nodes has no arcs connected to it. If the name of
the new child is not specified the system will generate a unique name of the form nodex.
graphNamenodelappendnode ?-key key? value
Appends a value (as a list) to one of the keyed values associated with an node. If no key is
specified, the key data is assumed.
graphNamenodeoppositenodearc
Return the node at the other end of the specified arc, which has to be adjacent to the given node.
graphNamenodesetnode ?-key key? ?value?
Set or get one of the keyed values associated with a node. If no key is specified, the key data
is assumed. Each node that is added to a graph has the empty string assigned to the key data
automatically. A node may have any number of keyed values associated with it. If value is not
specified, this command returns the current value assigned to the key; if value is specified, this
command assigns that value to the key.
graphNamenodeunsetnode ?-key key?
Remove a keyed value from the node node. If no key is specified, the key data is assumed.
graphNamenodes ?-key key? ?-value value? ?-in|-out|-adj|-inner|-embedding nodelist?
Return a list of nodes in the graph. Restrictions can limit the list of returned nodes based on
neighboring nodes, or based on the keyed values associated with the node. The restrictions that
involve neighboring nodes have a list of nodes as argument, specified after the name of the
restriction itself.
The possible restrictions are the same as for method arcs. The set of nodes to return is computed
as the union of all source and target nodes for all the arcs satisfying the restriction as defined
for arcs.
graphNameget ?-key key?
Return the value associated with the key key for the graph. If no key is specified, the key data
is assumed.
graphNamegetall
Returns a serialized list of key/value pairs (suitable for use with [arrayset]) for the whole
graph.
graphNamekeys
Returns a list of keys for the whole graph.
graphNamekeyexists ?-key key?
Return true if the specified key exists for the whole graph. If no key is specified, the key data
is assumed.
graphNameset ?-key key? ?value?
Set or get one of the keyed values associated with a graph. If no key is specified, the key data
is assumed. Each graph has the empty string assigned to the key data automatically. A graph may
have any number of keyed values associated with it. If value is not specified, this command
returns the current value assigned to the key; if value is specified, this command assigns that
value to the key.
graphNameswapnode1node2
Swap the position of node1 and node2 in the graph.
graphNameunset ?-key key?
Remove a keyed value from the graph. If no key is specified, the key data is assumed.
graphNamewalknode ?-order order? ?-type type? ?-dir direction? -command cmd
Perform a breadth-first or depth-first walk of the graph starting at the node node going in either
the direction of outgoing or opposite to the incoming arcs.
The type of walk, breadth-first or depth-first, is determined by the value of type; bfs indicates
breadth-first, dfs indicates depth-first. Depth-first is the default.
The order of the walk, pre-order, post-order or both-order is determined by the value of order;
pre indicates pre-order, post indicates post-order, both indicates both-order. Pre-order is the
default. Pre-order walking means that a node is visited before any of its neighbors (as defined by
the direction, see below). Post-order walking means that a parent is visited after any of its
neighbors. Both-order walking means that a node is visited before and after any of its neighbors.
The combination of a bread-first walk with post- or both-order is illegal.
The direction of the walk is determined by the value of dir; backward indicates the direction
opposite to the incoming arcs, forward indicates the direction of the outgoing arcs.
As the walk progresses, the command cmd will be evaluated at each node, with the mode of the call
(enter or leave) and values graphName and the name of the current node appended. For a pre-order
walk, all nodes are entered, for a post-order all nodes are left. In a both-order walk the first
visit of a node enters it, the second visit leaves it.
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