struct::tree(n)               Tcl Data Structures              struct::tree(n)



______________________________________________________________________________

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 ...?
              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
              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
              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])
              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 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
              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
              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
              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:

              o      The superfluous option -command has been removed.

              o      Ditto for the place holders. Instead of the placeholders
                     two loop variables have to be specified to contain node
                     and action information.

              o      The old command argument has been documented as a script
                     now, which it was in the past too.

              o      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 SF Trackers
       [http://sourceforge.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(n)
