Load some data from JSON file with IF statement HTML

I am using d3 to create a simple force graph where the data is loaded from a json file graph.json:

{
    "nodes": [
    {
      "user": "John Smith",
      "id": 0,
      "influence": 30, 
      "keywords":[["hello", 190], ["regards", 189], ["writing", 139], ["computer", 134], ["this", 133], ["thanks", 131]]
    },
    {
      "user": "Mary Brown",
      "id": 1,
      "influence": 15,
      "keywords":[["plane", 190], ["car", 13], ["truck", 13], ["bike", 13], ["motor", 190], ["engine", 12], ["regards", 12]]
    },
    {
      "user": "Joe Young",
      "id": 2,
      "influence": 50
      }
    ],

    "links": [
    {
      "id": 0,
      "source": 0,
      "target": 1,
      "weight": 5,
      "keywords":[["facebook", 18], ["twitter", 190], ["youtube", 18], ["instagram", 18], ["snapchat", 190], ["whatsapp", 17], ["vibe", 17]]
    },
    {
      "id": 1,
      "source": 1,
      "target": 2,
      "weight": 50
    },
    {
      "id": 2,
      "source": 2,
      "target": 0,
      "weight": 21
    }
  ]
}

However, I want to show only the nodes where their influence is greater or equal to 30. I tried using this if statement inside the .data() function, but it does not work:

var node = svg.selectAll(".node")
                .data(json.nodes, function(d){                    
                    if (d.influence >= 30)
                        return d;
                })

What am I doing wrong?

Here is the full code:

d3.json("graph.json", function(json) {     
            force
                .nodes(json.nodes)
                .links(json.links)
                .start();

            var link = svg.selectAll(".link")
                .data(json.links)
                .enter().append("line")
                .attr("class", "link")
                .style("stroke-width", function(d) { return Math.sqrt(d.weight); })

            var node = svg.selectAll(".node")
                .data(json.nodes, function(d){                    
                    if (d.influence >= 30)
                        return d;
                })
                .enter()
                .append("g")
                .attr("class", "node")
                .attr("pointer-events", "none")
                .call(force.drag)


            node.append("text")
                .attr("dx", 12)
                .attr("dy", ".35em")
                .attr("font-size", function(d){ return d.influence*1.5>9? d.influence*1.5: 9; })//text size
                .text(function(d) { return d.user });


            node.append("circle")
                .attr("r",function(d){ return d.influence/2 ? d.influence :5 ; })// node size
                .attr("fill", function(d){ return c10(d.id); }); //colour


            force.on("tick", function(d) {       

                node.attr("r", function(d){ return d.influence; })
                    .attr("cx", function(d){ return d.x; })
                    .attr("cy", function(d){ return d.y; });
                node.attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; });

                link.attr("x1", function(d) { return d.source.x; })
                    .attr("y1", function(d) { return d.source.y; })
                    .attr("x2", function(d) { return d.target.x; })
                    .attr("y2", function(d) { return d.target.y; });

            }); 
           force.start();        
        });