AverageCalculator

const products = [
  { name: 'A', group: 'G1', cost: 20.1 },
  { name: 'B', group: 'G2', cost: 98.4 },
  { name: 'C', group: 'G1', cost: 49.7 },
  { name: 'D', group: 'G3', cost: 35.8 },
  { name: 'E', group: 'G3', cost: 105.5 },
  { name: 'F', group: 'G1', cost: 55.2 },
  { name: 'G', group: 'G3', cost: 12.7 },
  { name: 'H', group: 'G1', cost: 88.6 },
  { name: 'I', group: 'G2', cost: 5.2 },
  { name: 'J', group: 'G2', cost: 15.3 },
];

const categories = [
  { name: 'C1', from: 0, to: 25 },
  { name: 'C2', from: 25, to: 50 },
  { name: 'C3', from: 50, to: 75 },
  { name: 'C4', from: 75, to: 100 },
  { name: 'C5', from: 100, to: null },
];

const margins = [
  { name: 'C1', margin: '20%' },
  { name: 'C2', margin: '30%' },
  { name: 'C3', margin: '0.4' },
  { name: 'C4', margin: '50%' },
  { name: 'C5', margin: '0.6' },
];

const averageCalculator = name => {
  // Devuelve la categoría del producto
  const categoryFinder = product => categories.filter(item => product.cost >= item.from && product.cost < item.to);

  // Devuelve el margen de la categoría
  const marginFinder = category => margins.filter(item => category.name == item.name);

  // Filtra o selecciona los productos solicitados ejem: 'G1'
  const grouped = products.filter(item => item.group == name);

  // Crea un array con los precios calculados para el grupo seleccionado
  const costCollection = grouped.map(item => {
    const catValue = categoryFinder(item);
    const marValue = marginFinder(catValue[0]);
    margin = numParser(marValue[0].margin);

    return item.cost * (1 + margin);
  });

  // Suma el total de precios del grupo seleccionado
  const totalSum = costCollection.reduce((sum, value) => sum + value);

  // Retorna el promedio
  return totalSum / grouped.length;
};

const numParser = strNumber => {
  let number = strNumber;
  const size = number.length;

  // Expresiones Regulares
  const rxPercent = /%/;
  const rxDot = /\./;

  // Valida el stringNumber con las RegExp
  const withSymbol = rxPercent.test(number);
  const isFloat = rxDot.test(number);

  // Elimina el simbolo porcentaje %
  if (withSymbol) {
    number = number.substr(0, size - 1);
  }

  // retorna float si tiene punto o entero si no.
  return number = isFloat ? parseFloat(number) : parseInt(number);
};

console.log(averageCalculator('G1'));