@technobuddha/library/src/dice-coefficient.ts

A large library of useful functions

import { compareStrings } from './compare-strings.ts';

/**
 * Options for the {@link diceCoefficient} function
 * @group String
 * @category Fuzzy Match
 */
export type DiceCoefficientOptions = {
  /** compare the two strings in case insensitive mode */
  caseInsensitive?: boolean;
};

/**
 * Compute the dice coefficient measure of similarity between two strings
 * @param input - The first string
 * @param compareTo - The second string
 * @param __nameParameters - see {@link DiceCoefficientOptions}
 * @returns a number from 0 (not similar) to 1 (equal) measuring the similarity
 * @group String
 * @category Fuzzy Match
 */
export function diceCoefficient(
  input: string,
  compareTo: string,
  { caseInsensitive = false }: DiceCoefficientOptions = {},
): number {
  if (input.length <= 1 || compareTo.length <= 1) {
    return compareStrings(input, compareTo, { caseInsensitive }) === 0 ? 1.0 : 0.0;
  }

  const bg0 = biGrams(caseInsensitive ? input.toLocaleLowerCase() : input);
  const bg1 = biGrams(caseInsensitive ? compareTo.toLocaleLowerCase() : compareTo);
  let count = 0;

  for (const bg of bg0) {
    const pos = bg1.indexOf(bg);
    if (pos >= 0) {
      count += 1;
      bg1[pos] = null;
    }
  }

  return (count * 2) / (bg0.length + bg1.length);
}

/**
 * Generates an array of bigrams (2-character substrings) from the given input string.
 * @param input - The string from which to generate bigrams.
 * @returns An array of bigrams extracted from the input string.
 * @internal
 */
function biGrams(input: string): (string | null)[] {
  const biGram = [] as string[];

  for (let i = 0; i < input.length - 1; ++i) {
    biGram.push(input.slice(i, i + 2));
  }
  return biGram;
}