CODE EXAMPLE FOR PYTHON

groupby

function groupBy(array, keyFn) {
  return array.reduce((accumulator, value) => {
    const key = keyFn(value);
    if (!accumulator[key]) {
      accumulator[key] = [value];
    } else {
      accumulator[key] = [value];
    }
    return accumulator;
  }, {});
}