D3 How to create a new array form multi level object?

Question

I am new from D3 (using v3) I have a data structure like below:

var data=[
{"name":"airport","values":[
        {"x":zero ,"y":333},
        {"x":one,"y":138},
        {"x":two,"y":118}
    ]},
{"name":"train","values":[
        {"x":zero,"y":136},
        {"x":one,"y":217},
        {"x":two,"y":109}
    ]},
{"name":"car","values":[
        {"x":zero,"y":132},
        {"x":one,"y":244},
        {"x":two,"y":145}
    ]}
]

I would like to use data.map to re-map an array like the follow format

["zero", "one", "two"]

what is the correct way to get only x value to form an array in d3?

Many thanks

Answer 1

I have made changes in "x" values as following i have just added "" to every element. As it is not number it will be treated as string

        {"x":"zero","y":333},
        {"x":"one","y":138},
        {"x":"two","y":118}

In your case, you can just add

d3.scale.ordinal().domain(data[0].values.map(function(element){
        return element.x
}))

It will give you array as you were expecting ["zero", "one", "two"].

Above solution is for when you have fix x labels but if you wish to traverse through each element to see or add more you can use this approach or for generic solution

d3.scale.ordinal().domain(filter(data))

function filter(localData){
  var tempdata = []
  localData.forEach(function (element){
      return element.values.forEach(function(element){
        tempdata.push(element.x)
    })
  })
  var uniqueArray = tempdata.filter(function(item, pos, self) {
    return self.indexOf(item) == pos;
  })
  return uniqueArray
}