merging selections

<!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>

<body>
  <script>
    // Feel free to change or delete any of the code you see in this editor!
    var svg = d3.select("body").append("svg")
      .attr("width", 960)
      .attr("height", 500)
		
    var dataFirst = [
      {ldap: "enjalot", x: 0},
      {ldap: "siumei", x: 1},
      {ldap: "ramesh", x: 2}
     ]
    
    var dataLater = [
      {ldap: "sami", x: 3},
      {ldap: "logan", x: 4},
      {ldap: "phillip", x: 5},
      {ldap: "siumei", x: 6}
    ];
    
    svg.selectAll("circle")
    	.data(dataFirst, function(d) {
      	return d.ldap;
    })
    		.enter()
    			.append("circle")
    			.attr("r", 30)
    			.attr("cx", function(d, i) {
      			return 50 + i * 80
    			})
    			.attr("cy",100)
    			.attr("fill", "#eda39a")
    .on("mouseover", function(d) {
      console.log(d);
    })
    
    setTimeout(function() {
      var circles = svg.selectAll("circle")
      	.data(dataLater, function(d){
        return d.ldap;
      });
      
      var enteredCircles = circles
      	.enter()
      		.append("circle")
    			.attr("r", 30)
    			.attr("cx", function(d, i) {
      			return 50 + d.x * 80
    			})
    			.attr("cy",100)
    			.attr("fill", "#862417");
      
      enteredCircles.merge(circles)
      	.attr("cx", function(d, i){
      		return 50 + d.x * 80                    
      })
      .style("stroke", "#111")
      	
    }, 1000)
    
    
  </script>
</body>

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