# Yada: Yet Another Double-Array
[](https://crates.io/crates/yada)
[](https://docs.rs/yada)
Yada is a yet another double-array trie library aiming for fast search and
compact data representation.
## Features
- Build static double-array tries
- Yada adopts the compact binary representation of double-array nodes like
[Darts-clone](https://github.com/s-yata/darts-clone).
- Common prefix search
- The method returns an `Iterator` that is an effective way to find multiple
values without heap allocation.
- Exact match search
- The method finds a value associated with an exact match key as a `Option`.
## Requirements
- Rust version >= 1.46.0
## Usage
See also [example code](examples/build_and_search.rs) for more details.
### Build a double-array trie
```rust
use yada::builder::DoubleArrayBuilder;
// make a keyset which have key-value pairs
let keyset = &[
("a".as_bytes(), 0),
("ab".as_bytes(), 1),
("abc".as_bytes(), 2),
("b".as_bytes(), 3),
("bc".as_bytes(), 4),
("c".as_bytes(), 5),
];
// build a double-array trie binary
let da_bytes: Option<Vec<u8>> = DoubleArrayBuilder::build(keyset);
```
### Search entries by keys
```rust
use yada::DoubleArray;
// create a double-array trie instance
let da = DoubleArray::new(da_bytes.unwrap());
// exact match search
for (key, value) in keyset {
assert_eq!(da.exact_match_search(key), Some(*value as u32));
}
assert_eq!(da.exact_match_search("abc".as_bytes()), Some(2));
assert_eq!(da.exact_match_search("abcd".as_bytes()), None);
// common prefix search
assert_eq!(
da.common_prefix_search("abcd".as_bytes())
.collect::<Vec<_>>(),
vec![(0, 1), (1, 2), (2, 3)] // match "a", "ab", "abc", value and key length
);
assert_eq!(
da.common_prefix_search("d".as_bytes()).collect::<Vec<_>>(),
vec![] // don't match
);
```
## Limitations
- The value must be represented as a 31 bit unsigned integer, typed `u32`.
- Yada uses the most significant bit (MSB) as a flag to distinguish between a value node and others.
- The offset of an double-array node is 29 bits wide, so it can represent up to
~536M nodes.
- It means this limitation results in the size upper bound ~2GB of double-arrays.
## License
Licensed under either of
- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE))
- MIT license ([LICENSE-MIT](LICENSE-MIT))
at your option.
## Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.
## References
- [Aoe, J. An Efficient Digital Search Algorithm by Using a Double-Array Structure.
IEEE Transactions on Software Engineering. Vol. 15, 9 (Sep 1989). pp. 1066-1077.](https://ieeexplore.ieee.org/document/31365)
- [Darts: Double ARray Trie System](http://chasen.org/~taku/software/darts/)
- [Darts-clone: A clone of Darts (Double-ARray Trie System)](https://github.com/s-yata/darts-clone)