en/builder/src/echarts3/processor/dataSample.js

var samplers = {
  average: function (frame) {
    var sum = 0;
    var count = 0;

    for (var i = 0; i < frame.length; i++) {
      if (!isNaN(frame[i])) {
        sum += frame[i];
        count++;
      }
    } // Return NaN if count is 0


    return count === 0 ? NaN : sum / count;
  },
  sum: function (frame) {
    var sum = 0;

    for (var i = 0; i < frame.length; i++) {
      // Ignore NaN
      sum += frame[i] || 0;
    }

    return sum;
  },
  max: function (frame) {
    var max = -Infinity;

    for (var i = 0; i < frame.length; i++) {
      frame[i] > max && (max = frame[i]);
    }

    return max;
  },
  min: function (frame) {
    var min = Infinity;

    for (var i = 0; i < frame.length; i++) {
      frame[i] < min && (min = frame[i]);
    }

    return min;
  },
  // TODO
  // Median
  nearest: function (frame) {
    return frame[0];
  }
};

var indexSampler = function (frame, value) {
  return Math.round(frame.length / 2);
};

export default function (seriesType, ecModel, api) {
  ecModel.eachSeriesByType(seriesType, function (seriesModel) {
    var data = seriesModel.getData();
    var sampling = seriesModel.get('sampling');
    var coordSys = seriesModel.coordinateSystem; // Only cartesian2d support down sampling

    if (coordSys.type === 'cartesian2d' && sampling) {
      var baseAxis = coordSys.getBaseAxis();
      var valueAxis = coordSys.getOtherAxis(baseAxis);
      var extent = baseAxis.getExtent(); // Coordinste system has been resized

      var size = extent[1] - extent[0];
      var rate = Math.round(data.count() / size);

      if (rate > 1) {
        var sampler;

        if (typeof sampling === 'string') {
          sampler = samplers[sampling];
        } else if (typeof sampling === 'function') {
          sampler = sampling;
        }

        if (sampler) {
          data = data.downSample(valueAxis.dim, 1 / rate, sampler, indexSampler);
          seriesModel.setData(data);
        }
      }
    }
  }, this);
}