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 addition 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 differences:
- [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
version 2.0, due to backward incompatible changes in the API of this module.
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
initialized 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 traversal 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 containing
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 children, 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 ...?
- Removes 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
containing all nodes descending from node, and passing the filter,
if such was specified.
This is actually the same as " treeName children
-all". descendants 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
- Returns 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]) containing
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
specified 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 children, 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
node x, 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
children), false otherwise.
- treeName lappend node key value
- Appends a value (as a list) to one of the keyed values associated
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, persistence, 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 necessarily 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
- Removes 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 loopvar. 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 various 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 simplified.
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
argument 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,
deserialize, =, 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 circumstances. 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 Trackers [
http://core.tcl.tk/tcllib/reportlist]. 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) 2002-2004,2012 Andreas Kupries <andreas_kupries@users.sourceforge.net>