新卒エンジニアが感じたChain of Responsibilityの魅力と実装 – KENTEM TechBlog

type Data = { label: string[] | null, value: number[][] | null };
type Processor = (data: Data, next: (v: Data) => Data) => Data;

const handleMissing: Processor = ({ value, label }, next) => {
  if (!(value && label)) throw new Error("Invalid data in handleMissing");
  try {
    const colMeans = value[0].map((_, col) => {
      const validValues = value
        .map(row => row[col])
        .filter(v => !Number.isNaN(v));
      const sum = validValues.reduce((a, b) => a + b, 0);
      return sum / validValues.length;
    });
    const filled = value.map(row =>
      row.map((v, i) => Number.isNaN(v) ? colMeans[i] : v)
    );
    return next({ value: filled, label });
  } catch {
    throw new Error("Error in handleMissing");
  }
};

const handleScaling: Processor = ({ value, label }, next) => {
  if (!(value && label)) throw new Error("Invalid data in scale");
  try {
    const min = value[0].map((_, col) => {
      const colValues = value.map(row => row[col]).filter(v => !Number.isNaN(v));
      return Math.min(...colValues);
    });
    const max = value[0].map((_, col) => {
      const colValues = value.map(row => row[col]).filter(v => !Number.isNaN(v));
      return Math.max(...colValues);
    });
    const scaled = value.map(row =>
      row.map((v, i) => {
        if (Number.isNaN(v)) return 0;
        const range = max[i] - min[i];
        if (range === 0) return 0;
        return (v - min[i]) / range;
      })
    );
    return next({ value: scaled, label });
  } catch {
    throw new Error("Error in scale");
  }
};

const handleEncodeLabels: Processor = ({ value, label }, next) => {
  if (!(value && label)) throw new Error("Invalid data in encodeLabels");
  try {
    const classes = Array.from(new Set(label));
    const encoded = label.map(label => classes.indexOf(label).toString());
    return next({ value, label: encoded });
  } catch {
    throw new Error("Error in encodeLabels");
  }
};

const valueArray = [
  [5.1, 3.5, 1.4, 0.2],
  [4.9, NaN, 1.4, 0.2],
  [7.0, 3.2, 4.7, NaN]
];
const labelArray = ["setosa", "virginica", "versicolor"];

const chainArray = [
  handleMissing,
  handleScaling,
  handleEncodeLabels
];


const dispatch = (value: Data, i: number): Data => {
  if (i >= chainArray.length) {
    return value;
  }
  const response = chainArray[i];
  return response(value, (v) => dispatch(v, i + 1));
}

const preprocessChain = (value: Data): Data | undefined => {
  try {
    return dispatch(value, 0);
  } catch (error) {
    console.error("Error in preprocessChain:", error);
    return undefined;
  }
}
const result = preprocessChain({ value: valueArray, label: labelArray });
console.log(result);