If you build a Tree in pre-order, and display in pre-order,
this is the tree for you.
No extra fluff, just a simple & performant one-trick pony.
Note: The tree depends on the build order, so is not possible to re-order the tree (changing parents or levels) in a different order. So, for example, you can't add a branch later to one in the middle (only can add after the end...).
Instead of creating a Tree of Node pointers, nested enums, or nested Arena-based ids, it just stores the representation of a Tree:
bash
. Users
├── jhon_doe
├ ├── file1.rs
├ ├── file2.rs
├── jane_doe
└────── cat.jpg
... flattened in pre-order on 3 vectors, that store the data, the level & the parent:
| DATA: | Users | jhondoe | file1.rs | file2.rs | janedoe | cat.jpg | |---------|-------|----------|----------|----------|----------|---------| | LEVEl: | 0 | 1 | 2 | 2 | 1 | 2 | | PARENT: | 0 | 0 | 1 | 1 | 0 | 4 |
This allows for the performance of Rust Vec, on the most common operations
(critically: Push items + Iterate), and very efficient iterations of
node::Node::parents/node::Node::children/node::Node::siblings, because it just traverses the flat vectors.
The iterators exploit these observations:
So this means that in the case of navigating the children of jhon_doe:
bash
. Users ⇡ parents
├── jhon_doe Index: 1, Level: 1
⇩ children start at
jhon_doe + 1,
level > jhon_doe
├ ├── file1.rs : Level 2 is child!
├ ├── file2.rs : Level 2 is child!
├── jane_doe : Level 1 is below, stop!
└────── cat.jpg
With this, instead of searching a potentially large array, it jumps directly after the node and iterates as long the nodes are above it!.
```rust use tree_flat::prelude::*;
let mut tree = Tree::with_capacity("Users", 6);
let mut root = tree.treerootmut();
let mut child = root.push("jhon_doe"); child.push("file1.rs"); child.push("file2.rs");
let mut child = root.push("jane_doe"); child.push("cat.jpg");
//The data is backed by vectors and arena-like ids on them: asserteq!( tree.asdata(), ["Users", "jhondoe", "file1.rs", "file2.rs", "janedoe", "cat.jpg",] ); asserteq!(tree.aslevel(), [0, 1, 2, 2, 1, 2,]); asserteq!(tree.asparents(), [0, 0, 1, 1, 0, 4,]); //Pretty print the tree println!("{}", tree);
// Iterations is as inserted: for f in &tree { dbg!(f); }
```
More info at my blog .
Inspired by the talk:
“High-performance Tree Wrangling, the APL Way” -- Aaron Hsu - APL Wiki
Contributions, issues, and feature requests are welcome!
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