@analys/table-timeseries-differential/dist/index.mjs

import { roundD2 } from '@aryth/math';
import { isNumeric } from '@typen/num-strict';
import { Differentiator } from '@vect/vector-differentiator';
import { iterate } from '@vect/vector-mapper';

// import { Table }          from '@analys/table'
const timeseriesDifferential = function ({
  dateLabel = 'date',
  fields,
  mutate = true
}) {
  /** @type {Table} */
  const table = mutate ? this : this.copy();
  const dateIndex = table.coin(dateLabel);
  const indexes = table.columnIndexes(fields),
        depth = indexes.length;
  if (indexes.includes(dateIndex)) indexes.splice(indexes.indexOf(dateIndex), 1);
  const rows = table.rows;
  let pv, cv, prevNum, currNum;

  for (const [prev, curr] of Differentiator.build(rows)) if (equalYear(prev[dateIndex], curr[dateIndex])) {
    iterate(indexes, i => {
      prevNum = isNumeric(pv = prev[i]), currNum = isNumeric(cv = curr[i]);

      if (prevNum) {
        if (currNum) {
          prev[i] = roundD2(pv - cv);
        } else {
          curr[i] = 0;
        }
      } else {
        if (currNum) {
          prev[i] = roundD2(0 - cv);
        } else {
          prev[i] = null;
        }
      }
    }, depth);
  }

  return rows.pop(), table.boot({
    rows
  });
};

const equalYear = (a, b) => a.slice(0, 4) === b.slice(0, 4);

export { timeseriesDifferential };