I am loading records into a crossfilter object by doing looped ajax calls :

```
    for (i=0;i<rangeToLoad.length;i++) {

    url = "http://myserver/"+rangeToLoad[i]+"/myrecords.js"

    $.ajax({
        url: url,
        dataType:"json",
        success: function (jsondata) {

            var records = jsondata.records;
            var parseDate = d3.time.format("%Y-%m-%d").parse;

            records.forEach(function(d) {
                d.date = parseDate(d.date);
            });

            if (typeof myCrossfilter === "undefined") { //first call
                myCrossfilter = crossfilter(records);
            } else {
                myCrossfilter.add(records);
            }

            initData();
            showData();
        }
    });
}

```

My `initData()` function is basically where the dimensions and groups of my crossfilter objects are defined.

```
dims.date = myCrossfilter.dimension(function(d) {return(+d.date);});
groups.date={};
dims.date2 = myCrossfilter.dimension(function(d) {return(+d.date);});
groups.date2={};
dims.instrumenttype = myCrossfilter.dimension(function(d) {return(d.product);});
groups.instrumenttype = {};
groups.date.pnlSum = dims.date.group().reduceSum(function(d) {return(d.pnl);});
groups.date2.cumPnlSum = dims.date2.group().reduceSum(function(d) {return(d.cumpnl);});
groups.instrumenttype.pnlSum = dims.instrumenttype.group().reduceSum(function(d) {return(d.pnl);});

```

My guess is that instead of updating the existing dimension for each ajax call, a new dimension is created each time.

How can I prevent that from happening ?