LevenshteinOcr.ts

/* code based on pseudocode from https://en.wikipedia.org/wiki/Wagner%E2%80%93Fischer_algorithm#Calculating_distance */
interface replacePair {
  first: string;
  second: string;
  cost: number
}

class replacePairCollection {
  replacePairs: Array<replacePair>;

  constructor(_replacePairs: Array<replacePair>) {
    this.replacePairs = _replacePairs;
  }

  inCollection(first: string, second: string): boolean {
    for (let replacePair of this.replacePairs)
      if ((first === replacePair.first) && (second === replacePair.second))
        return true;
    return false;
  }
  getCost(first: string, second: string): number {
    for (let replacePair of this.replacePairs)
      if ((first === replacePair.first) && (second === replacePair.second))
        return replacePair.cost;
  }
}

interface costObject {
  replacePairs: replacePairCollection;
  defaultReplaceCost: number;
  deleteCost: number;
  insertCost: number
}

export default function LevenshteinOCR(fromString: string, toString: string, override: costObject) {
  const fromLength: number = fromString.length;
  const toLength: number = toString.length;

  var distanceArray: Array<number>;

  for (let i = 1; i <= fromLength; i++)  distanceArray[i, 0] = i;
  for (let j = 1; j <= toLength; j++)    distanceArray[j, 0] = j;

  for (let j = 1; j <= toLength; j++)
    for (let i = 1; i <= fromLength; i++)
      distanceArray[i, j] =
        Math.min(
          distanceArray[i - 1, j - 1] + fromString[i - 1] === fromString[j - 1]
            ? 0
            : (override.replacePairs.inCollection(fromString[i - 1], fromString[j - 1])
              ? override.replacePairs.getCost(fromString[i - 1], fromString[j - 1])
              : override.defaultReplaceCost),
          distanceArray[i - 1, j] + override.deleteCost,
          distanceArray[i, j - 1] + override.insertCost);
  return distanceArray[toLength, fromLength];
}