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MinHashPermutations

The permutation coefficients a MinHash signature is built from.

public sealed class MinHashPermutations

Example — four permutations, supplied rather than seeded.

using Lodestar.Text.Similarity;

ulong[] multipliers = [3, 5, 7, 11];
ulong[] addends = [13, 17, 19, 23];
var permutations = new MinHashPermutations(multipliers, addends);

int count = permutations.Count;  // => 4
ulong first = permutations.Multiplier(0);  // => 3
MinHashScheme read = permutations.Scheme;  // => Legacy

Example — the same shape under the reference's current default, which reads 32-bit coefficients and needs an odd multiplier.

using Lodestar.Text.Similarity;

ulong[] odd = [3, 5, 7, 11];
ulong[] addends = [13, 17, 19, 23];
var affine = new MinHashPermutations(odd, addends, MinHashScheme.Affine32);

MinHashScheme scheme = affine.Scheme;  // => Affine32

Members — one page each.

Member	What it does
MinHashPermutations.Multiplier	The a coefficient of one permutation
MinHashPermutations.Addend	The b coefficient of one permutation

Remarks — the permutations are an input, not a seed. That is the same call decision 0004 made for randomized SVD's Ω, and for the same reason: a randomized algorithm whose randomness is supplied is an ordinary parity target, where one deriving it from a seed would have to reproduce another library's generator stream to agree with it.

datasketch exposes its own pair as MinHash.permutations, so a caller comparing against it passes those; a caller who only needs some permutations can pass any values, and two indexes compared against each other must use the same ones.

The scheme travels with the coefficients, because they are chosen together. An MinHashScheme.Affine32 multiplier is odd and fits 32 bits where a Legacy one spans 61, so the two families cannot share a set — and reading one family's coefficients through the other's arithmetic produces a signature rather than an error, which is why the constructor refuses the mismatch instead of computing it.

Naming no scheme means Legacy, so a signature built before affine32 existed keeps comparing to one built after.

Applies to — net10.0, netstandard2.0.

See also — MinHash, MinHashScheme, the set-similarity index.