pie.value([value])
If value is specified, sets the value accessor to the specified function or number and returns this pie generator. If value is not specified, returns the current value accessor, which defaults to:
function value(d) {
return d;
}
When a pie is generated, the value accessor will be invoked for each element in the input data array, being passed the element d, the index i, and the array data as three arguments. The default value accessor assumes that the input data are numbe