[javascript] group by

group-by.js

/**
 *
 * @param {Object[]} dataset
 * @param {string} key
 * @returns {Object.<string, Object[]>}
 * @example groupBy([
 *   {scope: 'step:1', name: 'API'},
 *   {scope: 'step:1', name: 'amount'},
 *   {scope: 'step:2', name: 'Solvent'}
 * ], 'scope') => {
 *   'step:1': [{ scope: 'step:1', name: 'API' }, { scope: 'step:1', name: 'amount' }],
 *   'step:2': [{ scope: 'step:2', name: 'Solvent' }]
 * }
 */
export default function groupBy(dataset, key) {
  return dataset.reduce(function (rv, x) {
    (rv[x[key]] = rv[x[key]] || []).push(x);
    return rv;
  }, {});
}