Triply, a triply-linked list lib

Yet another data structure for creating trees.

Install

npm i triply

Usage

const Triply = require("../lib/triply").Triply;
 
// NOTE only objects are valid entries
// which will be formatted using reserved keys.
// Here we use `data` to insert a number
const node = new Triply({data:1})
    .push({data:2}) // just append a sibling, the insertion point is moved to the new node
    .open({data:3}) // make the insertion point a branch and append a new child
    .close() // try to move the insertion point to the parent
    .push({data:4}) // append another sibling
    .previous() // try to move the insertion point back along the traversal path (the branch containing `data:2`)
    .open({data:5}) // append another child
    .push({data:6}); // append another sibling to that child
 
// traverse the tree (lazy iterator)
// we have to keep track of branch 'closers' (compare for example with XML closing tags)
for(let x of node.traverse()) console.log("x",Triply.isClose(x) ? "closes: " + Triply.link(x).data : x.data);

License

License

API documentation

• Triply Class
• Functional implementation

About

Triply is a way to create in-memory trees with some very interesting performance characteristics:

• Fast traversal in 2 directions
• Fast appendChild, insertBefore, insertAfter, removeChild
• Fast access to siblings
• Fast access to the parent at the first or last child

Updates require writes to at most 4 pointers (5 when expanding or collapsing branches).

Use Triply to create trees that can be modified with some ease.

Triply Pointer Rules

• 1 = depth-first traversal
• 2 = reversed traversal
• 3 = open/close link

Traversal directions (invert directions and arrows for reversed traversal):

• UP = BRANCH -> LEAF or BRANCH
• DOWN = BRANCH or LEAF -> CLOSE
• SAME = LEAF -> LEAF

Tree Diagrams

           L
     1 // 2 1 \\ 2
      B 3-><-3 /B
  1 // 2      1 \\ 2
   B 3---> <---3 /B 1 --> <-- 2 B ~

Append a child at tier 1 (or a sibling at tier 2):

         L 1 --> <-- 2 L
     1 // 2          1 \\ 2
      B 3--->     <---3 /B
  1 // 2               1 \\ 2
   B 3--->          <---3 /B 1 --> <-- 2 B ~

Append a child at tier 0 (or a sibling at tier 1):

         L 1 --> <-- 2 L                   L
     1 // 2          1 \\ 2          1 // 2 1 \\ 2
      B 3--->     <---3 /B 1--> <-- 2 B 3-><-3 /B
  1 // 2                                      1 \\ 2
   B 3--->                                 <---3 /B 1 --> <-- 2 B ~

Access logic

• firstChild: follow 1 from BRANCH
• lastChild: follow 3 to find CLOSE and then 2
• nextSibling: follow 1 from LEAF or 3 + 1 from BRANCH
• previousSibling: follow 2, if found CLOSE follow 3
• parent (O[no of siblings]): follow 2 from firstSibling or 1 + 3 from lastSibling
• firstChildTest: child -> 2 === BRANCH
• lastChildTest: child -> 1 === CLOSE

NOTE: Accessing the parent is only relevant for insertBefore when it's the first child.