javascript - Highcharts: Custom dataGrouping approximation: dataGroups cropped by chart area -

see example custom approximation provided highcharts: http://jsfiddle.net/gh/get/library/pure/highcharts/highcharts/tree/master/samples/stock/plotoptions/series-datagrouping-approximation

datagrouping: {     approximation: function () {         return this.datagroupinfo.length;     },     forced: true }, 

scroll selection left right.

notice datagroupinfo.length increases , decreases datagroup enters , exits chart area. believe due datagroup being cropped chart area.

i have attempted resolve issue setting cropthreshold infinity without success (it seems unrelated).

i need create custom approximation not cropped chart area.

to complicate things bit, custom approximation series[0] , average. in case, result of series[0] divided series[1].

my current attempt following:
http://jsfiddle.net/rbwc217s/

approximation: function(arr) {     var numerator = 0,         denominator = 0;     if (arr.length !== 0) {         var start = this.xdata.indexof(this.processedxdata[0]) + this.datagroupinfo.start,             slicedarr = this.chart.series[1].ydata.slice(start, start + (arr.length));         (var in arr) {             numerator += arr[i];             denominator += slicedarr[i];         };     };     return denominator !== 0 ? math.round((numerator / denominator) * 1000) / 1000 : null; }, 

it works expected - except on edge of chart area. again, believe due datagroup being cropped chart area.

any appreciated.
thank you.