#vec #indexes #map


A compact key-value map for unique but not dense indexes

5 releases

0.1.4 Mar 22, 2022
0.1.3 Mar 22, 2022
0.1.2 Mar 22, 2022
0.1.1 Mar 15, 2022
0.1.0 Mar 14, 2022

#620 in Data structures

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crates.io docs.rs

A small utility crate when you have a list of unique but not dense indexes for which to each you want to associates a value. In the documentation the indexes are referred as key. Not an indexed map!

It can be considered a slower but more compact version of BTreeMap.


A brief example of the crate's capacities

use map_of_indexes::{MapOfIndexes, MapOfIndexesError, KeyValue};

let v = vec![(3, 4), (1, 2), (5, 6)];
let mut map: MapOfIndexes::<(u8, u16)> = v.try_into()?;

let push_res = map.push_checked((0,9));
assert_eq!(push_res, Err(MapOfIndexesError::SmallerKey));

let old_key_value = map.set((1,9))?;
assert_eq!(old_key_value.key(), &1);
assert_eq!(old_key_value.value(), &2);

CombinedKeyValue is a compact representation when you need to save space.

use map_of_indexes::{CombinedKeyValue};
// We have keys that take up to 40 bits, and value up to 24;
// Using (u64, u64) would have wasted 8 byte per entry.
type CombinedU64 = CombinedKeyValue<u64, 40, 24>;
CombinedU64::safety_check(); // ensure that key and value size fit on the unsigned integer.

let v = vec![CombinedU64::new(3u64, 4u32), CombinedU64::new(1u64, 2u32), CombinedU64::new(5u64, 6u32)];
let map: MapOfIndexes<_> = v.try_into()?;
let inner_raw: Vec<u64> = Vec::from_iter(map.iter().map(|x| *x.as_ref()));
assert_eq!(inner_raw, vec![2199023255553, 4398046511107, 6597069766661]);

For an even more compact representation, consider using the bitvec crate.

License: AGPL-3.0+


~26K SLoC