Single country with dropdown & radio buttons

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>

<form id="dimensions">
  <input  type='radio' id="income" name="mode" checked>Income</input>
  <input type='radio' id="population" name="mode">Population</input>
	<input type='radio' id="lifeExpectancy" name="mode">Life Expectancy</input>
</form>
  <script>
    
// To-dos:        
// Add second country
// Get rid of the commas on the X-axis labels
    
var margin = {top: 20, right: 30, bottom: 60, left: 20}; 
    // I added 50 to the bottom margin to make room for the dropdown and the radio buttons at the top
    // I added 40 to the left margin to make room for the y-axis tick marks to show
    // I added 20 to the right margin to make the chart fit within view
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;
   
var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
		.append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
    
var  g = svg.append("g").attr("transform", "translate(" + margin.left + "," + margin.top + ")");
    
var line = d3.line()
	.x(function(d){return x(d[0])})
	.y(function(d){return y(d[1])})

function filterJSON(json, location, dim){
	    var result = [];
  json.forEach( function(val, idx, arr){
    if(val.name == location){
      result.push(val[dim])}
  })
	return result[0];
}

var x = d3.scaleLinear()
    	.range([0,width])
var y = d3.scaleLinear()
    	.range([height,0])

var data;

var yearStyle = {
    "decimal": ".",
        "thousands": "",
        "grouping": [3],
        "currency": ["$", ""]
}

// Here I tried to create a custom locale format to get rid of the commas in the years, but it did not work
//var yearStyle = d3.formatLocale(yearStyle);
    
function drawGraph(data, dim){
  x.domain(d3.extent(data, function(d){return d[0]}))
  y.domain(d3.extent(data, function(d){return d[1]}))
  //appends x axis
  g.append("g")
    .attr("id", "xaxis")
  	.attr("transform", "translate(0," + height + ")")
  	.call(d3.axisBottom(x)
         //.tickFormat(yearStyle) // This replaces the years with [object Object], instead of showing the years without the commas, like I wanted
          )
  	.append("text")
    .attr("fill", "#000")
  	.text("Year")
    .attr("transform", "translate(" + [width - margin.right, 0 - margin.bottom/2 + 25] + ")")
  // appends y axis
  g.append("g")
    	.attr("id", "yaxis")
  	.call(d3.axisLeft(y))
  		.append("text")
      .attr("fill", "#000")
      .attr("transform", "rotate(-90)")
      .attr("transform", "translate(" + [margin.left * 0.5, margin.top] + ") rotate(" + -90 + ")")
      .attr("text-anchor", "end")
      .text(dim);  
  // appends line
	g.append("path")
  	.datum(data)
    .attr("fill", "none")
  	.attr("class","line")
    .attr("stroke", "green")
    .attr("stroke-width", 1)
  	.attr("d", line);
}

d3.json("nations.json", function(error,json){
  if (error) throw error;
  
  function changeIt(){
    //get rid of everything and re-draw
    	d3.selectAll(".line").remove()
      d3.selectAll("#yaxis").remove()
      d3.selectAll("#xaxis").remove()
    //get the value from the dropdown
  		var sect = document.getElementById("ddSel");
      var country = sect.options[sect.selectedIndex].value;
      var form = document.getElementById("dimensions")
      var form_val;
    	for(var i=0; i<form.length; i++){
        if(form[i].checked){
          form_val = form[i].id;}}
      data = filterJSON(json, country, form_val)
      drawGraph(data, form_val)      
            }
  var dropdown = d3.select("select")
  	.attr("id", "ddSel");
  
  var options = dropdown.selectAll("option")
  	.data(json)
    
  options.enter()
    .append("option")
    .text(function(d){return d.name})
		dropdown.on("change",changeIt)
    
	var dataDim = d3.select("#dimensions")
	dataDim.on("change", changeIt)
  
  data = filterJSON(json, "Angola", "income")
  console.log(line(data))
  drawGraph(data, "income")
  
});

</script>
</body>

https://d3js.org/d3.v4.min.js