Function groupData

_benchmarks/sample_echarts.js:7880–7892

* Group a list by key.

(array, getKey // return key
    )

     */

    function groupData(array, getKey // return key
    ) {
      var buckets = createHashMap();
      var keys = [];
      each(array, function (item) {
        var key = getKey(item);
        (buckets.get(key) || (keys.push(key), buckets.set(key, []))).push(item);
      });
      return {
        keys: keys,
        buckets: buckets
      };
    }
    /**
     * Interpolate raw values of a series with percent
     *