Text osa normalizeddistance

Osa.NormalizedDistance

Scales the distance into [0, 1] by dividing it by the length of the longer input.

public static double NormalizedDistance(ReadOnlySpan<char> a, ReadOnlySpan<char> b, TextElement element = TextElement.Utf16Unit)

Parameters — a and b are the two strings to compare; element says what counts as one character, and it moves both the distance and the lengths it is divided by.

Returns — double in [0, 1]: 0 when the two are equal, 1 when nothing can be reused. Two empty inputs give 0.

Example — one swap over four characters.

using Lodestar.Text.Distances;

double d = Osa.NormalizedDistance("abcd", "acbd");   // => 0.25

Remarks — the divisor is max(len(a), len(b)), the same as Levenshtein and DamerauLevenshtein use, so thresholds move freely between those three. Indel is the one that does not share the scale.

The trap is a consequence of the swap being cheap: this scores a pair with several transpositions much closer to 0 than Levenshtein.NormalizedDistance does on the same pair, so a threshold carried over from Levenshtein will let more through than you expect. That is the intended behaviour and worth knowing about anyway.

Applies to — net10.0, netstandard2.0.

See also — Osa.Distance, Osa.NormalizedSimilarity, DamerauLevenshtein.NormalizedDistance, the Python equivalence table.