Struct sparsevec::SparseVec [−][src]
pub struct SparseVec<T> { /* fields omitted */ }
Expand description
A SparseVec efficiently encodes a two-dimensional matrix of integers. The input matrix must be encoded as a one-dimensional vector of integers with a row-length. Given an “empty” value, the SparseVec uses row displacement to compress that value as described in “Storing a sparse table” by Robert Endre Tarjan and Andrew Chi-Chih Yao. Afterwards it encodes the result further using a PackedVec.
Example
extern crate sparsevec;
use sparsevec::SparseVec;
fn main() {
let v:Vec<usize> = vec![1,0,0,0,
0,0,7,8,
9,0,0,3];
let sv = SparseVec::from(&v, 0, 4);
assert_eq!(sv.get(0,0).unwrap(), 1);
assert_eq!(sv.get(1,2).unwrap(), 7);
assert_eq!(sv.get(2,3).unwrap(), 3);
}
How it works
Let’s take as an example the two-dimensional vector
1 0 0
2 0 0
3 0 0
0 0 4
represented as a one dimensional vector v = [1,0,0,2,0,0,3,0,0,0,0,4]
with row-length 3.
Storing this vector in memory is wasteful as the majority of its elements is 0. We can compress
this vector using row displacement, which merges all rows into a vector such that non-zero
entries are never mapped to the same position. For the above example, this would result in the
compressed vector c = [1,2,3,0,4]
:
1 0 0
2 0 0
3 0 0
0 0 4
---------
1 2 3 0 4
To retrieve values from the compressed vector, we need a displacement vector, which
describes how much each row was shifted during the compression. For the above example, the
displacement vector would be d = [0, 1, 2, 2]
. In order to retrieve the value at
position (2, 0), we can calculate its compressed position with pos = d[row] + col
:
pos = d[2] + 0 // =2
value = c[pos] // =3
Implementations
impl<T: Clone + Copy + PartialEq> SparseVec<T> where
T: AsPrimitive<usize> + FromPrimitive + Ord + PrimInt + ToPrimitive + Unsigned,
usize: AsPrimitive<T>,
impl<T: Clone + Copy + PartialEq> SparseVec<T> where
T: AsPrimitive<usize> + FromPrimitive + Ord + PrimInt + ToPrimitive + Unsigned,
usize: AsPrimitive<T>,
Constructs a new SparseVec from a Vec
of unsigned integers where empty_val
describes
the values to be compressed and row_length
the element size per row in the original
two-dimensional vector.
Examples
use sparsevec::SparseVec;
let v:Vec<usize> = vec![1,2,3,4,5,6,7,8];
let sv = SparseVec::from(&v, 0, 4);
assert_eq!(sv.get(1,2).unwrap(), 7);
Returns the value of the element at position (r,c)
, where r
is a row and c
is a
column. Returns None
if out of bounds.
Examples
use sparsevec::SparseVec;
let v:Vec<usize> = vec![1,2,3,4,5,6,7,8];
let sv = SparseVec::from(&v, 0, 4);
assert_eq!(sv.get(1,2).unwrap(), 7);
Returns the number of elements of the original input vector.
Examples
use sparsevec::SparseVec;
let v = vec![1,2,3,4];
let sv = SparseVec::from(&v, 0 as usize, 2);
assert_eq!(sv.len(), 4);