function nearestNeighbor(neighbors) {
  var xValue = function(d) { return d[0]; },
      yValue = function(d) { return d[1]; },
      voronoi = d3.geom.voronoi().x(xValue).y(yValue),
      polygons = voronoi(neighbors);

  function nearest(point) {

    return polygons.filter(function(polygon) { 
      return polygonContainsPoint(polygon, normalize(point)); 
    })[0].point;
    
  }

  function normalize(point) {
    return [xValue(point), yValue(point)]
  }

  function polygonContainsPoint(points, test) {
    var result = false;
    for (i = 0, j = points.length - 1; i < points.length; j = i++) {
      if ((points[i][1] > test[1]) != (points[j][1] > test[1]) &&
      (test[0] < (points[j][0] - points[i][0]) * (test[1] - points[i][1]) / (points[j][1]-points[i][1]) + points[i][0])) {
        result = !result;
      }
    }
    return result;
  }

  nearest.x = function(_) {
    if (!arguments.length) return xValue;
    xValue = _;
    voronoi = voronoi.x(xValue);
    polygons = voronoi(neighbors);
    return nearest;
  };

  nearest.y = function(_) {
    if (!arguments.length) return yValue;
    yValue = _;
    voronoi = voronoi.y(yValue);
    polygons = voronoi(neighbors);
    return nearest;
  };

  nearest.clipExtent = function(_) {
    if(!arguments.length) return voronoi.clipExtent();
    voronoi = voronoi.clipExtent(_);
    polygons = voronoi(neighbors);
    return nearest;
  }

  return nearest;
}