struct::tree(3tcl) Tcl Data Structures struct::tree(3tcl)______________________________________________________________________________NAME
struct::tree - Create and manipulate tree objects
SYNOPSIS
package require Tcl 8.2
package require struct::tree ?2.1.1?
package require struct::list ?1.5?
::struct::tree ?treeName? ?=|:=|as|deserialize source?
treeName option ?arg arg ...?
::struct::tree::prune
treeName = sourcetree
treeName --> desttree
treeName ancestors node
treeName append node key value
treeName attr key
treeName attr key -nodes list
treeName attr key -glob globpattern
treeName attr key -regexp repattern
treeName children ?-all? node ?filter cmdprefix?
treeName cut node
treeName delete node ?node ...?
treeName depth node
treeName descendants node ?filter cmdprefix?
treeName deserialize serialization
treeName destroy
treeName exists node
treeName get node key
treeName getall node ?pattern?
treeName keys node ?pattern?
treeName keyexists node key
treeName index node
treeName insert parent index ?child ?child ...??
treeName isleaf node
treeName lappend node key value
treeName leaves
treeName move parent index node ?node ...?
treeName next node
treeName numchildren node
treeName nodes
treeName parent node
treeName previous node
treeName rename node newname
treeName rootname
treeName serialize ?node?
treeName set node key ?value?
treeName size ?node?
treeName splice parent from ?to? ?child?
treeName swap node1 node2
treeName unset node key
treeName walk node ?-order order? ?-type type? loopvar script
treeName walkproc node ?-order order? ?-type type? cmdprefix
_________________________________________________________________DESCRIPTION
A tree is a collection of named elements, called nodes, one of which is
distinguished as a root, along with a relation ("parenthood") that
places a hierarchical structure on the nodes. (Data Structures and
Algorithms; Aho, Hopcroft and Ullman; Addison-Wesley, 1987). In addi‐
tion to maintaining the node relationships, this tree implementation
allows any number of keyed values to be associated with each node.
The element names can be arbitrary strings.
A tree is thus similar to an array, but with three important differ‐
ences:
[1] Trees are accessed through an object command, whereas arrays are
accessed as variables. (This means trees cannot be local to a
procedure.)
[2] Trees have a hierarchical structure, whereas an array is just an
unordered collection.
[3] Each node of a tree has a separate collection of attributes and
values. This is like an array where every value is a dictionary.
Note: The major version of the package struct has been changed to ver‐
sion 2.0, due to backward incompatible changes in the API of this mod‐
ule. Please read the section Changes for 2.0 for a full list of all
changes, incompatible and otherwise.
API
TREE CLASS API
The main commands of the package are:
::struct::tree ?treeName? ?=|:=|as|deserialize source?
The command creates a new tree object with an associated global
Tcl command whose name is treeName. This command may be used to
invoke various operations on the tree. It has the following
general form:
treeName option ?arg arg ...?
Option and the args determine the exact behavior of the
command.
If treeName is not specified a unique name will be generated by the
package itself. If a source is specified the new tree will be initial‐
ized to it. For the operators =, :=, and as source is interpreted as
the name of another tree object, and the assignment operator = will be
executed. For deserialize the source is a serialized tree object and
deserialize will be executed.
In other words
::struct::tree mytree = b
is equivalent to
::struct::tree mytree
mytree = b
and
::struct::tree mytree deserialize $b
is equivalent to
::struct::tree mytree
mytree deserialize $b
::struct::tree::prune
This command is provided outside of the tree methods, as it is
not a tree method per se. It however interacts tightly with the
method walk. When used in the walk script it causes the traver‐
sal to ignore the children of the node we are currently at.
This command cannot be used with the traversal modes which look
at children before their parent, i.e. post and in. The only
applicable orders of traversal are pre and both. An error is
thrown if the command and chosen order of traversal do not fit.
TREE OBJECT API
Two general observations beforehand:
[1] The root node of the tree can be used in most places where a
node is asked for. The default name of the rootnode is "root",
but this can be changed with the method rename (see below).
Whatever the current name for the root node of the tree is, it
can be retrieved by calling the method rootname.
[2] The method insert is the only way to create new nodes, and they
are automatically added to a parent. A tree object cannot have
nodes without a parent, save the root node.
And now the methods supported by tree objects created by this package:
treeName = sourcetree
This is the assignment operator for tree objects. It copies the
tree contained in the tree object sourcetree over the tree data
in treeName. The old contents of treeName are deleted by this
operation.
This operation is in effect equivalent to
treeName deserialize [sourcetree serialize]
treeName --> desttree
This is the reverse assignment operator for tree objects. It
copies the tree contained in the tree object treeName over the
tree data in the object desttree. The old contents of desttree
are deleted by this operation.
This operation is in effect equivalent to
desttree deserialize [treeName serialize]
treeName ancestors node
This method extends the method parent and returns a list con‐
taining all ancestor nodes to the specified node. The immediate
ancestor, in other words, parent node, is the first element in
that list, its parent the second element, and so on until the
root node is reached, making it the last element of the returned
list.
treeName append node key value
Appends a value to one of the keyed values associated with an
node. Returns the new value given to the attribute key.
treeName attr key
treeName attr key -nodes list
treeName attr key -glob globpattern
treeName attr key -regexp repattern
This method retrieves the value of the attribute named key, for
all nodes in the tree (matching the restriction specified via
one of the possible options) and having the specified attribute.
The result is a dictionary mapping from node names to the value
of attribute key at that node. Nodes not having the attribute
key, or not passing a specified restriction, are not listed in
the result.
The possible restrictions are:
-nodes The value is a list of nodes. Only the nodes mentioned in
this list are searched for the attribute.
-glob The value is a glob pattern. Only the nodes in the tree
whose names match this pattern are searched for the
attribute.
-regexp
The value is a regular expression. Only the nodes in the
tree whose names match this pattern are searched for the
attribute.
treeName children ?-all? node ?filter cmdprefix?
Return a list of the children of node. If the option -all is
specified, then not only the direct children, but their chil‐
dren, and so on are returned in the result. If a filter command
is specified only those nodes are listed in the final result
which pass the test. The command in cmdprefix is called with two
arguments, the name of the tree object, and the name of the node
in question. It is executed in the context of the caller and has
to return a boolean value. Nodes for which the command returns
false are removed from the result list before it is returned to
the caller.
Some examples:
mytree insert root end 0 ; mytree set 0 volume 30
mytree insert root end 1
mytree insert root end 2
mytree insert 0 end 3
mytree insert 0 end 4
mytree insert 4 end 5 ; mytree set 5 volume 50
mytree insert 4 end 6
proc vol {t n} {
$t keyexists $n volume
}
proc vgt40 {t n} {
if {![$t keyexists $n volume]} {return 0}
expr {[$t get $n volume] > 40}
}
tclsh> lsort [mytree children -all root filter vol]
0 5
tclsh> lsort [mytree children -all root filter vgt40]
5
tclsh> lsort [mytree children root filter vol]
0
tclsh> puts ([lsort [mytree children root filter vgt40]])
()
treeName cut node
Removes the node specified by node from the tree, but not its
children. The children of node are made children of the parent
of the node, at the index at which node was located.
treeName delete node ?node ...?
Remove the specified nodes from the tree. All of the nodes'
children will be removed as well to prevent orphaned nodes.
treeName depth node
Return the number of steps from node node to the root node.
treeName descendants node ?filter cmdprefix?
This method extends the method children and returns a list con‐
taining all nodes descending from node, and passing the filter,
if such was specified.
This is actually the same as "treeName children -all". descen‐
dants should be prefered, and "children -all" will be deprecated
sometime in the future.
treeName deserialize serialization
This is the complement to serialize. It replaces tree data in
treeName with the tree described by the serialization value. The
old contents of treeName are deleted by this operation.
treeName destroy
Destroy the tree, including its storage space and associated
command.
treeName exists node
Remove true if the specified node exists in the tree.
treeName get node key
Returns the value associated with the key key for the node node.
treeName getall node ?pattern?
Returns a dictionary (suitable for use with [array set]) con‐
taining the attribute data for the node. If the glob pattern is
specified only the attributes whose names match the pattern will
be part of the dictionary.
treeName keys node ?pattern?
Returns a list of keys for the node. If the pattern is speci‐
fied only the attributes whose names match the pattern will be
part of the returned list. The pattern is a glob pattern.
treeName keyexists node key
Return true if the specified key exists for the node.
treeName index node
Returns the index of node in its parent's list of children. For
example, if a node has nodeFoo, nodeBar, and nodeBaz as chil‐
dren, in that order, the index of nodeBar is 1.
treeName insert parent index ?child ?child ...??
Insert one or more nodes into the tree as children of the node
parent. The nodes will be added in the order they are given. If
parent is root, it refers to the root of the tree. The new nodes
will be added to the parent node's child list at the index given
by index. The index can be end in which case the new nodes will
be added after the current last child. Indices of the form
"end-n" are accepted as well.
If any of the specified children already exist in treeName,
those nodes will be moved from their original location to the
new location indicated by this command.
If no child is specified, a single node will be added, and a
name will be generated for the new node. The generated name is
of the form nodex, where x is a number. If names are specified
they must neither contain whitespace nor colons (":").
The return result from this command is a list of nodes added.
treeName isleaf node
Returns true if node is a leaf of the tree (if node has no chil‐
dren), false otherwise.
treeName lappend node key value
Appends a value (as a list) to one of the keyed values associ‐
ated with an node. Returns the new value given to the attribute
key.
treeName leaves
Return a list containing all leaf nodes known to the tree.
treeName move parent index node ?node ...?
Make the specified nodes children of parent, inserting them into
the parent's child list at the index given by index. Note that
the command will take all nodes out of the tree before inserting
them under the new parent, and that it determines the position
to place them into after the removal, before the re-insertion.
This behaviour is important when it comes to moving one or more
nodes to a different index without changing their parent node.
treeName next node
Return the right sibling of node, or the empty string if node
was the last child of its parent.
treeName numchildren node
Return the number of immediate children of node.
treeName nodes
Return a list containing all nodes known to the tree.
treeName parent node
Return the parent of node.
treeName previous node
Return the left sibling of node, or the empty string if node was
the first child of its parent.
treeName rename node newname
Renames the node node to newname. An error is thrown if either
the node does not exist, or a node with name newname does exist.
The result of the command is the new name of the node.
treeName rootname
Returns the name of the root node of the tree.
treeName serialize ?node?
This method serializes the sub-tree starting at node. In other
words it returns a tcl value completely describing the tree
starting at node. This allows, for example, the transfer of
tree objects (or parts thereof) over arbitrary channels, persis‐
tence, etc. This method is also the basis for both the copy
constructor and the assignment operator.
The result of this method has to be semantically identical over
all implementations of the tree interface. This is what will
enable us to copy tree data between different implementations of
the same interface.
The result is a list containing containing a multiple of three
elements. It is like a serialized array except that there are
two values following each key. They are the names of the nodes
in the serialized tree. The two values are a reference to the
parent node and the attribute data, in this order.
The reference to the parent node is the empty string for the
root node of the tree. For all other nodes it is the index of
the parent node in the list. This means that they are integers,
greater than or equal to zero, less than the length of the list,
and multiples of three. The order of the nodes in the list is
important insofar as it is used to reconstruct the lists of
children for each node. The children of a node have to be listed
in the serialization in the same order as they are listed in
their parent in the tree.
The attribute data of a node is a dictionary, i.e. a list of
even length containing a serialized array. For a node without
attribute data the dictionary is the empty list.
Note: While the current implementation returns the root node as
the first element of the list, followed by its children and
their children in a depth-first traversal this is not necessar‐
ily true for other implementations. The only information a
reader of the serialized data can rely on for the structure of
the tree is that the root node is signaled by the empty string
for the parent reference, that all other nodes refer to their
parent through the index in the list, and that children occur in
the same order as in their parent.
A possible serialization for the tree structure
+- d
+- a -+
root -+- b +- e
+- c
is
{root {} {} a 0 {} d 3 {} e 3 {} b 0 {} c 0 {}}
The above assumes that none of the nodes have attributes.
treeName set node key ?value?
Set or get one of the keyed values associated with a node. 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, and returns it.
treeName size ?node?
Return a count of the number of descendants of the node node; if
no node is specified, root is assumed.
treeName splice parent from ?to? ?child?
Insert a node named child into the tree as a child of the node
parent. If parent is root, it refers to the root of the tree.
The new node will be added to the parent node's child list at
the index given by from. The children of parent which are in
the range of the indices from and to are made children of child.
If the value of to is not specified it defaults to end. If no
name is given for child, a name will be generated for the new
node. The generated name is of the form nodex, where x is a
number. The return result from this command is the name of the
new node.
The arguments from and to are regular list indices, i.e. the
form "end-n" is accepted as well.
treeName swap node1 node2
Swap the position of node1 and node2 in the tree.
treeName unset node key
Remove a keyed value from the node node. The method will do
nothing if the key does not exist.
treeName walk node ?-order order? ?-type type? loopvar script
Perform a breadth-first or depth-first walk of the tree starting
at the node node. 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-, post-, both- or in-order
is determined by the value of order; pre indicates pre-order,
post indicates post-order, both indicates both-order and in
indicates in-order. Pre-order is the default.
Pre-order walking means that a parent node is visited before any
of its children. For example, a breadth-first search starting
from the root will visit the root, followed by all of the root's
children, followed by all of the root's grandchildren. Post-
order walking means that a parent node is visited after any of
its children. Both-order walking means that a parent node is
visited before and after any of its children. In-order walking
means that a parent node is visited after its first child and
before the second. This is a generalization of in-order walking
for binary trees and will do the right thing if a binary tree is
walked. The combination of a breadth-first walk with in-order is
illegal.
As the walk progresses, the script will be evaluated at each
node. The evaluation takes place in the context of the caller of
the method. Regarding loop variables, these are listed in loop‐
var. If one only one variable is specified it will be set to the
id of the node. When two variables are specified, i.e. loopvar
is a true list, then the first variable will be set to the
action performed at the node, and the other to the id of the
node itself. All loop variables are created in the context of
the caller.
There are three possible actions: enter, leave, or visit. enter
actions occur during pre-order walks; leave actions occur during
post-order walks; visit actions occur during in-order walks. In
a both-order walk, the command will be evaluated twice for each
node; the action is enter for the first evaluation, and leave
for the second.
Note: The enter action for a node is always performed before the
walker will look at the children of that node. This means that
changes made by the script to the children of the node will
immediately influence the walker and the steps it will take.
Any other manipulation, for example of nodes higher in the tree
(i.e already visited), or upon leaving will have undefined
results. They may succeed, error out, silently compute the wrong
result, or anything in between.
At last a small table showing the relationship between the vari‐
ous options and the possible actions.
order type actions notes
-------------------
pre dfs enter parent before children
post dfs leave parent after children
in dfs visit parent between first and second child.
both dfs enter, leave parent before and after children
-------------------
pre bfs enter parent before children
post bfs leave parent after children
in bfs -- illegal --
both bfs enter, leave parent before and after children
-------------------
Note the command ::struct::tree::prune. This command can be used
in the walk script to force the command to ignore the children
of the node we are currently at. It will throw an error if the
order of traversal is either post or in as these modes visit the
children before their parent, making pruning non-sensical.
treeName walkproc node ?-order order? ?-type type? cmdprefix
This method is like method walk in all essentials, except the
interface to the user code. This method invokes a command prefix
with three additional arguments (tree, node, and action),
instead of evaluating a script and passing the node via a loop
variable.
CHANGES FOR 2.0
The following noteworthy changes have occurred:
[1] The API for accessing attributes and their values has been sim‐
plified.
All functionality regarding the default attribute "data" has
been removed. This default attribute does not exist anymore. All
accesses to attributes have to specify the name of the attribute
in question. This backward incompatible change allowed us to
simplify the signature of all methods handling attributes.
Especially the flag -key is not required anymore, even more, its
use is now forbidden. Please read the documentation for the
methods set, get, getall, unset, append, lappend, keyexists and
keys for a description of the new API's.
[2] The methods keys and getall now take an optional pattern argu‐
ment and will return only attribute data for keys matching this
pattern.
[3] Nodes can now be renamed. See the documentation for the method
rename.
[4] The structure has been extended with API's for the serialization
and deserialization of tree objects, and a number of operations
based on them (tree assignment, copy construction).
Please read the documentation for the methods serialize, deseri‐
alize, =, and -->, and the documentation on the construction of
tree objects.
Beyond the copying of whole tree objects these new API's also
enable the transfer of tree objects over arbitrary channels and
for easy persistence.
[5] The walker API has been streamlined and made more similar to the
command foreach. In detail:
· The superfluous option -command has been removed.
· Ditto for the place holders. Instead of the placeholders
two loop variables have to be specified to contain node
and action information.
· The old command argument has been documented as a script
now, which it was in the past too.
· The fact that enter actions are called before the walker
looks at the children of a node has been documented now.
In other words it is now officially allowed to manipulate
the list of children for a node under these circum‐
stances. It has been made clear that changes under any
other circumstances will have undefined results, from
silently computing the wrong result to erroring out.
[6] A new method, attr, was added allowing the query and retrieval
of attribute data without regard to the node relationship.
[7] The method children has been extended with the ability to select
from the children of the node based on an arbitrary filtering
criterium. Another extension is the ability to look not only at
the immediate children of the node, but the whole tree below it.
EXAMPLES
The following example demonstrates the creation of new nodes:
mytree insert root end 0 ; # Create node 0, as child of the root
mytree insert root end 1 2 ; # Ditto nodes 1 & 2
mytree insert 0 end 3 ; # Now create node 3 as child of node 0
mytree insert 0 end ; # Create another child of 0, with a
# generated name. The name is returned
# as the result of the command.
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain
bugs and other problems. Please report such in the category struct ::
tree of the Tcllib SF Trackers [http://source‐
forge.net/tracker/?group_id=12883]. Please also report any ideas for
enhancements you may have for either package and/or documentation.
KEYWORDS
breadth-first, depth-first, in-order, node, post-order, pre-order,
serialization, tree
CATEGORY
Data structures
COPYRIGHT
Copyright (c) 2002-2004 Andreas Kupries <andreas_kupries@users.sourceforge.net>
struct 2.1.1 struct::tree(3tcl)
