Accepted answer

v.Speed is always NaN in your current example. Because +x.Type attempts to convert a string like "Apple" into a number and fails. If you just want to count, then add or subtract 1 in your reducer, rather than v.Speed. Then you need to update your sel_stack code and chart code to handle this change, of course.

Here's a working example for the 2 types in your data. You'll have to update it to handle arbitrary numbers of types, probably by building an array of all your types up front and then looping through it to add stacks to the chart:

var data = [ {"Name":"Abby","Type":"Apple"}, {"Name":"Abby","Type":"Banana"}, {"Name":"Bob","Type":"Apple"} ]

var ndx = crossfilter(data)

var xdim = ndx.dimension(function (d) {return d.Name;});

In the reducer, just add and subtract 1 to count:

var ydim =
  function(p, v) {
    p[v.Type] = (p[v.Type] || 0) + 1;
    return p;}, 
  function(p, v) {
    p[v.Type] = (p[v.Type] || 0) - 1;
    return p;}, 
  function() {
    return {};

sel_stack no longer takes a number, but a key:

function sel_stack(valueKey) {
return function(d) {
  return d.value[valueKey];

var chart = dc.barChart("#chart");

Here we hard-code the stack key, for the purpose of the example:

  .group(ydim, "Apple", sel_stack('Apple'))

Again, the other hard-coded stack key. You'll need to recreate the loop after creating some sort of data structure that holds all of your stack values.

//for(var i = 2; i<6; ++i)
  chart.stack(ydim, 'Banana', sel_stack('Banana'));


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