{
   "ReturnCode":0,
   "ReturnMessage":"Success",
   "List":[{
         "Client":"Ad",
         "Department":"DP",
         "ProjectId":"12355",
         "ProjectName":"4940"
      }, {
         "Client":"Ad",
         "Department":"SP",
         "ProjectId":"12355",
         "ProjectName":"4940"
      }, {
         "Client":"Ad",
         "Department":"Co",
         "ProjectId":"12355",
         "ProjectName":"asdf"
      }, {
         "Client":"Ad",
         "Department":"Co",
         "ProjectId":"212355",
         "ProjectName":"45ed"
      }, {
         "Client":"Ad",
         "Department":"Co",
         "ProjectId":"212355",
         "ProjectName":"45ed "
      }, {
         "Client":"we",
         "Department":" SP ",
         "ProjectId":"123455",
         "ProjectName":"asdf"
      }, {
         "Client":"we",
         "Department":"Co",
         "ProjectId":"123455",
         "ProjectName":"asdf"
      }, {
         "Client":"oc",
         "Department":"Co",
         "ProjectId":"24355",
         "ProjectName":"qwe"
   }]
}

[{Key:”Ad”, value:2}, {Key:”we”, value:1}, {Key:”oc”, value:1}]

d3.json("json/data.json", function(data) {
    console.log(data);

    var nested_data = d3.nest()
    .key(function(d) { return d.Client; })
    .key(function(d) { return d.ProjectId; })
    .rollup(function(leaves) { return leaves.length; })
    .entries(data.List);

    console.log(nested_data);

    console.log(nested_data[0].values.length) //length of key 'AD'
})