Custom Grouping Functor

Properties of grouped objects are defined by an array. The first element of this array is a template with a property from original data, the second one – the functor which needs being applied to all values of this property in a group.

There are "sum", "max" and "min" functors. You may create your own functor – a function that gets two parameters:

the value template
an array with all data objects in a group

and returns the result value.

Let's take the example about sales of 4 companies described in the "Grouping" article. Here the "sum" functor was used to get the total sales of a company.

Let's now create a functor that will display the average sales. In this case grouping can be implemented as follows:

chart.group({
    by:"#company#",
    map:{
        sales:["#sales#",getAverage]
    }
});
 
function getAverage(prop,data){
    var count = data.length;
    var summ = 0; 
    for(var i = 0; i < count; i++){
        summ += parseFloat(data[i].sales);
    }
    return summ/count;
}