score:2

Accepted answer

Just set text-anchor attribute middle to the text element. This code would work even for nodes having different size.

node.append("text")
      .attr("text-anchor", "middle")
      .attr("dy", ".35em")
      .text(function(d) { return d.group });

Working snippet:

var width = 500,
  height = 500;

var color = d3.scale.category20();

var force = d3.layout.force()
  .charge(-120)
  .linkDistance(80)
  .size([width, height]);

var svg = d3.select("body").append("svg")
  .attr("width", width)
  .attr("height", height);

var mis = document.getElementById('mis').innerHTML;
graph = JSON.parse(mis);

force.nodes(graph.nodes)
  .links(graph.links)
  .start();

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

var node = svg.selectAll(".node")
  .data(graph.nodes)
  .enter().append("g")
  .attr("class", "node")
  .call(force.drag);

node.append("circle")
  .attr("r", function(d,i){ return i%2==0?10:8 })
  .style("fill", function(d) {
    return color(d.group);
  })

node.append("text")
  .attr("text-anchor", "middle")
  .attr("dy", ".35em")
  .text(function(d) {
    return d.group
  });

force.on("tick", function() {
  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;
    });

  d3.selectAll("circle").attr("cx", function(d) {
      return d.x;
    })
    .attr("cy", function(d) {
      return d.y;
    });

  d3.selectAll("text").attr("x", function(d) {
      return d.x;
    })
    .attr("y", function(d) {
      return d.y;
    });

});
.link {
  stroke: #ccc;
}

.node text {
  pointer-events: none;
  font: 10px sans-serif;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>
<script type="application/json" id="mis">
   { "nodes": [{ "name": "Myriel", "group": 1 }, { "name": "Napoleon", "group": 1 }, { "name": "Mlle.Baptistine", "group": 1 }, { "name": "Mme.Magloire", "group": 1 }, { "name": "CountessdeLo", "group": 1 }, { "name": "Geborand", "group": 1 }, { "name": "Champtercier", "group": 1 }, { "name": "Cravatte", "group": 1 }, { "name": "Count", "group": 1 }, { "name": "OldMan", "group": 1 }, { "name": "Labarre", "group": 2 }, { "name": "Valjean", "group": 2 }, { "name": "Marguerite", "group": 3 }, { "name": "Mme.deR", "group": 2 }, { "name": "Isabeau", "group": 2 }, { "name": "Gervais", "group": 2 }, { "name": "Tholomyes", "group": 3 }, { "name": "Listolier", "group": 3 }, { "name": "Fameuil", "group": 3 }, { "name": "Blacheville", "group": 3 }, { "name": "Favourite", "group": 3 }, { "name": "Dahlia", "group": 3 }, { "name": "Zephine", "group": 3 }, { "name": "Fantine", "group": 3 }, { "name": "Mme.Thenardier", "group": 4 }, { "name": "Thenardier", "group": 4 }, { "name": "Cosette", "group": 5 }, { "name": "Javert", "group": 4 }, { "name": "Fauchelevent", "group": 0 }, { "name": "Bamatabois", "group": 2 }, { "name": "Perpetue", "group": 3 }, { "name": "Simplice", "group": 2 }, { "name": "Scaufflaire", "group": 2 }, { "name": "Woman1", "group": 2 }, { "name": "Judge", "group": 2 }, { "name": "Champmathieu", "group": 2 }, { "name": "Brevet", "group": 2 }, { "name": "Chenildieu", "group": 2 }, { "name": "Cochepaille", "group": 2 }, { "name": "Pontmercy", "group": 4 }, { "name": "Boulatruelle", "group": 6 }, { "name": "Eponine", "group": 4 }, { "name": "Anzelma", "group": 4 }, { "name": "Woman2", "group": 5 }, { "name": "MotherInnocent", "group": 0 }, { "name": "Gribier", "group": 0 }, { "name": "Jondrette", "group": 7 }, { "name": "Mme.Burgon", "group": 7 }, { "name": "Gavroche", "group": 8 }, { "name": "Gillenormand", "group": 5 }, { "name": "Magnon", "group": 5 }, { "name": "Mlle.Gillenormand", "group": 5 }, { "name": "Mme.Pontmercy", "group": 5 }, { "name": "Mlle.Vaubois", "group": 5 }, { "name": "Lt.Gillenormand", "group": 5 }, { "name": "Marius", "group": 8 }, { "name": "BaronessT", "group": 5 }, { "name": "Mabeuf", "group": 8 }, { "name": "Enjolras", "group": 8 }, { "name": "Combeferre", "group": 8 }, { "name": "Prouvaire", "group": 8 }, { "name": "Feuilly", "group": 8 }, { "name": "Courfeyrac", "group": 8 }, { "name": "Bahorel", "group": 8 }, { "name": "Bossuet", "group": 8 }, { "name": "Joly", "group": 8 }, { "name": "Grantaire", "group": 8 }, { "name": "MotherPlutarch", "group": 9 }, { "name": "Gueulemer", "group": 4 }, { "name": "Babet", "group": 4 }, { "name": "Claquesous", "group": 4 }, { "name": "Montparnasse", "group": 4 }, { "name": "Toussaint", "group": 5 }, { "name": "Child1", "group": 10 }, { "name": "Child2", "group": 10 }, { "name": "Brujon", "group": 4 }, { "name": "Mme.Hucheloup", "group": 8 }], "links": [{ "source": 1, "target": 0, "value": 1 }, { "source": 2, "target": 0, "value": 8 }, { "source": 3, "target": 0, "value": 10 }, { "source": 3, "target": 2, "value": 6 }, { "source": 4, "target": 0, "value": 1 }, { "source": 5, "target": 0, "value": 1 }, { "source": 6, "target": 0, "value": 1 }, { "source": 7, "target": 0, "value": 1 }, { "source": 8, "target": 0, "value": 2 }, { "source": 9, "target": 0, "value": 1 }, { "source": 11, "target": 10, "value": 1 }, { "source": 11, "target": 3, "value": 3 }, { "source": 11, "target": 2, "value": 3 }, { "source": 11, "target": 0, "value": 5 }, { "source": 12, "target": 11, "value": 1 }, { "source": 13, "target": 11, "value": 1 }, { "source": 14, "target": 11, "value": 1 }, { "source": 15, "target": 11, "value": 1 }, { "source": 17, "target": 16, "value": 4 }, { "source": 18, "target": 16, "value": 4 }, { "source": 18, "target": 17, "value": 4 }, { "source": 19, "target": 16, "value": 4 }, { "source": 19, "target": 17, "value": 4 }, { "source": 19, "target": 18, "value": 4 }, { "source": 20, "target": 16, "value": 3 }, { "source": 20, "target": 17, "value": 3 }, { "source": 20, "target": 18, "value": 3 }, { "source": 20, "target": 19, "value": 4 }, { "source": 21, "target": 16, "value": 3 }, { "source": 21, "target": 17, "value": 3 }, { "source": 21, "target": 18, "value": 3 }, { "source": 21, "target": 19, "value": 3 }, { "source": 21, "target": 20, "value": 5 }, { "source": 22, "target": 16, "value": 3 }, { "source": 22, "target": 17, "value": 3 }, { "source": 22, "target": 18, "value": 3 }, { "source": 22, "target": 19, "value": 3 }, { "source": 22, "target": 20, "value": 4 }, { "source": 22, "target": 21, "value": 4 }, { "source": 23, "target": 16, "value": 3 }, { "source": 23, "target": 17, "value": 3 }, { "source": 23, "target": 18, "value": 3 }, { "source": 23, "target": 19, "value": 3 }, { "source": 23, "target": 20, "value": 4 }, { "source": 23, "target": 21, "value": 4 }, { "source": 23, "target": 22, "value": 4 }, { "source": 23, "target": 12, "value": 2 }, { "source": 23, "target": 11, "value": 9 }, { "source": 24, "target": 23, "value": 2 }, { "source": 24, "target": 11, "value": 7 }, { "source": 25, "target": 24, "value": 13 }, { "source": 25, "target": 23, "value": 1 }, { "source": 25, "target": 11, "value": 12 }, { "source": 26, "target": 24, "value": 4 }, { "source": 26, "target": 11, "value": 31 }, { "source": 26, "target": 16, "value": 1 }, { "source": 26, "target": 25, "value": 1 }, { "source": 27, "target": 11, "value": 17 }, { "source": 27, "target": 23, "value": 5 }, { "source": 27, "target": 25, "value": 5 }, { "source": 27, "target": 24, "value": 1 }, { "source": 27, "target": 26, "value": 1 }, { "source": 28, "target": 11, "value": 8 }, { "source": 28, "target": 27, "value": 1 }, { "source": 29, "target": 23, "value": 1 }, { "source": 29, "target": 27, "value": 1 }, { "source": 29, "target": 11, "value": 2 }, { "source": 30, "target": 23, "value": 1 }, { "source": 31, "target": 30, "value": 2 }, { "source": 31, "target": 11, "value": 3 }, { "source": 31, "target": 23, "value": 2 }, { "source": 31, "target": 27, "value": 1 }, { "source": 32, "target": 11, "value": 1 }, { "source": 33, "target": 11, "value": 2 }, { "source": 33, "target": 27, "value": 1 }, { "source": 34, "target": 11, "value": 3 }, { "source": 34, "target": 29, "value": 2 }, { "source": 35, "target": 11, "value": 3 }, { "source": 35, "target": 34, "value": 3 }, { "source": 35, "target": 29, "value": 2 }, { "source": 36, "target": 34, "value": 2 }, { "source": 36, "target": 35, "value": 2 }, { "source": 36, "target": 11, "value": 2 }, { "source": 36, "target": 29, "value": 1 }, { "source": 37, "target": 34, "value": 2 }, { "source": 37, "target": 35, "value": 2 }, { "source": 37, "target": 36, "value": 2 }, { "source": 37, "target": 11, "value": 2 }, { "source": 37, "target": 29, "value": 1 }, { "source": 38, "target": 34, "value": 2 }, { "source": 38, "target": 35, "value": 2 }, { "source": 38, "target": 36, "value": 2 }, { "source": 38, "target": 37, "value": 2 }, { "source": 38, "target": 11, "value": 2 }, { "source": 38, "target": 29, "value": 1 }, { "source": 39, "target": 25, "value": 1 }, { "source": 40, "target": 25, "value": 1 }, { "source": 41, "target": 24, "value": 2 }, { "source": 41, "target": 25, "value": 3 }, { "source": 42, "target": 41, "value": 2 }, { "source": 42, "target": 25, "value": 2 }, { "source": 42, "target": 24, "value": 1 }, { "source": 43, "target": 11, "value": 3 }, { "source": 43, "target": 26, "value": 1 }, { "source": 43, "target": 27, "value": 1 }, { "source": 44, "target": 28, "value": 3 }, { "source": 44, "target": 11, "value": 1 }, { "source": 45, "target": 28, "value": 2 }, { "source": 47, "target": 46, "value": 1 }, { "source": 48, "target": 47, "value": 2 }, { "source": 48, "target": 25, "value": 1 }, { "source": 48, "target": 27, "value": 1 }, { "source": 48, "target": 11, "value": 1 }, { "source": 49, "target": 26, "value": 3 }, { "source": 49, "target": 11, "value": 2 }, { "source": 50, "target": 49, "value": 1 }, { "source": 50, "target": 24, "value": 1 }, { "source": 51, "target": 49, "value": 9 }, { "source": 51, "target": 26, "value": 2 }, { "source": 51, "target": 11, "value": 2 }, { "source": 52, "target": 51, "value": 1 }, { "source": 52, "target": 39, "value": 1 }, { "source": 53, "target": 51, "value": 1 }, { "source": 54, "target": 51, "value": 2 }, { "source": 54, "target": 49, "value": 1 }, { "source": 54, "target": 26, "value": 1 }, { "source": 55, "target": 51, "value": 6 }, { "source": 55, "target": 49, "value": 12 }, { "source": 55, "target": 39, "value": 1 }, { "source": 55, "target": 54, "value": 1 }, { "source": 55, "target": 26, "value": 21 }, { "source": 55, "target": 11, "value": 19 }, { "source": 55, "target": 16, "value": 1 }, { "source": 55, "target": 25, "value": 2 }, { "source": 55, "target": 41, "value": 5 }, { "source": 55, "target": 48, "value": 4 }, { "source": 56, "target": 49, "value": 1 }, { "source": 56, "target": 55, "value": 1 }, { "source": 57, "target": 55, "value": 1 }, { "source": 57, "target": 41, "value": 1 }, { "source": 57, "target": 48, "value": 1 }, { "source": 58, "target": 55, "value": 7 }, { "source": 58, "target": 48, "value": 7 }, { "source": 58, "target": 27, "value": 6 }, { "source": 58, "target": 57, "value": 1 }, { "source": 58, "target": 11, "value": 4 }, { "source": 59, "target": 58, "value": 15 }, { "source": 59, "target": 55, "value": 5 }, { "source": 59, "target": 48, "value": 6 }, { "source": 59, "target": 57, "value": 2 }, { "source": 60, "target": 48, "value": 1 }, { "source": 60, "target": 58, "value": 4 }, { "source": 60, "target": 59, "value": 2 }, { "source": 61, "target": 48, "value": 2 }, { "source": 61, "target": 58, "value": 6 }, { "source": 61, "target": 60, "value": 2 }, { "source": 61, "target": 59, "value": 5 }, { "source": 61, "target": 57, "value": 1 }, { "source": 61, "target": 55, "value": 1 }, { "source": 62, "target": 55, "value": 9 }, { "source": 62, "target": 58, "value": 17 }, { "source": 62, "target": 59, "value": 13 }, { "source": 62, "target": 48, "value": 7 }, { "source": 62, "target": 57, "value": 2 }, { "source": 62, "target": 41, "value": 1 }, { "source": 62, "target": 61, "value": 6 }, { "source": 62, "target": 60, "value": 3 }, { "source": 63, "target": 59, "value": 5 }, { "source": 63, "target": 48, "value": 5 }, { "source": 63, "target": 62, "value": 6 }, { "source": 63, "target": 57, "value": 2 }, { "source": 63, "target": 58, "value": 4 }, { "source": 63, "target": 61, "value": 3 }, { "source": 63, "target": 60, "value": 2 }, { "source": 63, "target": 55, "value": 1 }, { "source": 64, "target": 55, "value": 5 }, { "source": 64, "target": 62, "value": 12 }, { "source": 64, "target": 48, "value": 5 }, { "source": 64, "target": 63, "value": 4 }, { "source": 64, "target": 58, "value": 10 }, { "source": 64, "target": 61, "value": 6 }, { "source": 64, "target": 60, "value": 2 }, { "source": 64, "target": 59, "value": 9 }, { "source": 64, "target": 57, "value": 1 }, { "source": 64, "target": 11, "value": 1 }, { "source": 65, "target": 63, "value": 5 }, { "source": 65, "target": 64, "value": 7 }, { "source": 65, "target": 48, "value": 3 }, { "source": 65, "target": 62, "value": 5 }, { "source": 65, "target": 58, "value": 5 }, { "source": 65, "target": 61, "value": 5 }, { "source": 65, "target": 60, "value": 2 }, { "source": 65, "target": 59, "value": 5 }, { "source": 65, "target": 57, "value": 1 }, { "source": 65, "target": 55, "value": 2 }, { "source": 66, "target": 64, "value": 3 }, { "source": 66, "target": 58, "value": 3 }, { "source": 66, "target": 59, "value": 1 }, { "source": 66, "target": 62, "value": 2 }, { "source": 66, "target": 65, "value": 2 }, { "source": 66, "target": 48, "value": 1 }, { "source": 66, "target": 63, "value": 1 }, { "source": 66, "target": 61, "value": 1 }, { "source": 66, "target": 60, "value": 1 }, { "source": 67, "target": 57, "value": 3 }, { "source": 68, "target": 25, "value": 5 }, { "source": 68, "target": 11, "value": 1 }, { "source": 68, "target": 24, "value": 1 }, { "source": 68, "target": 27, "value": 1 }, { "source": 68, "target": 48, "value": 1 }, { "source": 68, "target": 41, "value": 1 }, { "source": 69, "target": 25, "value": 6 }, { "source": 69, "target": 68, "value": 6 }, { "source": 69, "target": 11, "value": 1 }, { "source": 69, "target": 24, "value": 1 }, { "source": 69, "target": 27, "value": 2 }, { "source": 69, "target": 48, "value": 1 }, { "source": 69, "target": 41, "value": 1 }, { "source": 70, "target": 25, "value": 4 }, { "source": 70, "target": 69, "value": 4 }, { "source": 70, "target": 68, "value": 4 }, { "source": 70, "target": 11, "value": 1 }, { "source": 70, "target": 24, "value": 1 }, { "source": 70, "target": 27, "value": 1 }, { "source": 70, "target": 41, "value": 1 }, { "source": 70, "target": 58, "value": 1 }, { "source": 71, "target": 27, "value": 1 }, { "source": 71, "target": 69, "value": 2 }, { "source": 71, "target": 68, "value": 2 }, { "source": 71, "target": 70, "value": 2 }, { "source": 71, "target": 11, "value": 1 }, { "source": 71, "target": 48, "value": 1 }, { "source": 71, "target": 41, "value": 1 }, { "source": 71, "target": 25, "value": 1 }, { "source": 72, "target": 26, "value": 2 }, { "source": 72, "target": 27, "value": 1 }, { "source": 72, "target": 11, "value": 1 }, { "source": 73, "target": 48, "value": 2 }, { "source": 74, "target": 48, "value": 2 }, { "source": 74, "target": 73, "value": 3 }, { "source": 75, "target": 69, "value": 3 }, { "source": 75, "target": 68, "value": 3 }, { "source": 75, "target": 25, "value": 3 }, { "source": 75, "target": 48, "value": 1 }, { "source": 75, "target": 41, "value": 1 }, { "source": 75, "target": 70, "value": 1 }, { "source": 75, "target": 71, "value": 1 }, { "source": 76, "target": 64, "value": 1 }, { "source": 76, "target": 65, "value": 1 }, { "source": 76, "target": 66, "value": 1 }, { "source": 76, "target": 63, "value": 1 }, { "source": 76, "target": 62, "value": 1 }, { "source": 76, "target": 48, "value": 1 }, { "source": 76, "target": 58, "value": 1 }] }
</script>

score:0

It works after changing the position of dx;

node.append("text")
      .attr("dx", -2)
      .attr("dy", ".35em")
      .text(function(d) { return d.group });

enter image description here

Here is the updated fiddle.

score:2

You can tamper the dx and dy to move it to the center something like this.

node.append("text")
      .attr("dx", function(d) { if(d.group > 9) {return -5.5} else {return -1.5;} })
      .attr("dy", ".3em")
      .text(function(d) { return d.group });

What this does is if the group is 9 then single digit then return -1.5 else for 2 digit return -5.5.

Working code here

Hope this helps!


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