nvd3/src/models/lineWithFourAxes.js

nv.models.lineWithLegend = function() {
  var margin = {top: 60, right: 60, bottom: 40, left: 60},
      getWidth = function() { return 960 },
      getHeight = function() { return 500 },
      dotRadius = function() { return 2.5 },
      getX = function(d) { return d.x },
      getY = function(d) { return d.y },
      color = d3.scale.category20().range(),
      dispatch = d3.dispatch('tooltipShow', 'tooltipHide');

  var x = d3.scale.linear(),
      y = d3.scale.linear(),
      xAxis = nv.models.axis().scale(x).orient('bottom'),
      yAxis = nv.models.axis().scale(y).orient('left'),
      x2Axis = nv.models.axis().scale(x).orient('top'),
      y2Axis = nv.models.axis().scale(y).orient('right'),
      legend = nv.models.legend().height(30),
      lines = nv.models.line();


  function chart(selection) {
    selection.each(function(data) {
      var width = getWidth(),
          height = getHeight(),
          availableWidth = width - margin.left - margin.right,
          availableHeight = height - margin.top - margin.bottom;

      var series = data.filter(function(d) { return !d.disabled })
            .map(function(d) { 
              return d.values.map(function(d,i) {
                return { x: getX(d,i), y: getY(d,i) }
              })
            });

      x   .domain(d3.extent(d3.merge(series), function(d) { return d.x } ))
          .range([0, availableWidth]);

      y   .domain(d3.extent(d3.merge(series), function(d) { return d.y } ))
          .range([availableHeight, 0]);

      lines
        .width(availableWidth)
        .height(availableHeight)
        .color(data.map(function(d,i) {
          return d.color || color[i % 10];
        }).filter(function(d,i) { return !data[i].disabled }))


      var wrap = d3.select(this).selectAll('g.wrap').data([data]);
      var gEnter = wrap.enter().append('g').attr('class', 'wrap d3lineWithLegend').append('g');

      gEnter.append('g').attr('class', 'x axis');
      gEnter.append('g').attr('class', 'y axis');
      gEnter.append('g').attr('class', 'x2 axis');
      gEnter.append('g').attr('class', 'y2 axis');
      gEnter.append('g').attr('class', 'linesWrap');
      gEnter.append('g').attr('class', 'legendWrap');


      legend.dispatch.on('legendClick', function(d,i) { 
        d.disabled = !d.disabled;

        if (!data.filter(function(d) { return !d.disabled }).length) {
          data.map(function(d) {
            d.disabled = false;
            wrap.selectAll('.series').classed('disabled', false);
            return d;
          });
        }

        selection.transition().call(chart);
      });

/*
      //
      legend.dispatch.on('legendMouseover', function(d, i) {
        d.hover = true;
        selection.transition().call(chart)
      });

      legend.dispatch.on('legendMouseout', function(d, i) {
        d.hover = false;
        selection.transition().call(chart)
      });
*/

      lines.dispatch.on('pointMouseover.tooltip', function(e) {
        dispatch.tooltipShow({
          point: e.point,
          series: e.series,
          pos: [e.pos[0] + margin.left, e.pos[1] + margin.top],
          seriesIndex: e.seriesIndex,
          pointIndex: e.pointIndex
        });
      });

      lines.dispatch.on('pointMouseout.tooltip', function(e) {
        dispatch.tooltipHide(e);
      });


      //TODO: margins should be adjusted based on what components are used: axes, axis labels, legend
      margin.top = legend.height() + 20; // 20 is for the x2 axis...  this should be done in a better place, but just doing this to show the 4 axes in an example

      var g = wrap.select('g')
          .attr('transform', 'translate(' + margin.left + ',' + margin.top + ')');


      legend.width(width/2 - margin.right);

      g.select('.legendWrap')
          .datum(data)
          .attr('transform', 'translate(' + (width/2 - margin.left) + ',' + (-margin.top) +')')
          .call(legend);


      var linesWrap = g.select('.linesWrap')
          .datum(data.filter(function(d) { return !d.disabled }))


      d3.transition(linesWrap).call(lines);


      xAxis
        .domain(x.domain())
        .range(x.range())
        .ticks( width / 100 )
        .tickSize(-availableHeight, 0);

      g.select('.x.axis')
          .attr('transform', 'translate(0,' + y.range()[0] + ')');
      d3.transition(g.select('.x.axis'))
          .call(xAxis);

      yAxis
        .domain(y.domain())
        .range(y.range())
        .ticks( height / 36 )
        .tickSize(-availableWidth, 0);

      d3.transition(g.select('.y.axis'))
          .call(yAxis);

      x2Axis
        .domain(x.domain())
        .range(x.range())
        .ticks( width / 100 )
        .tickSize(-availableHeight, 0);

      d3.transition(g.select('.x2.axis'))
          .call(x2Axis);

      y2Axis
        .domain(y.domain())
        .range(y.range())
        .ticks( height / 36 )
        .tickSize(-availableWidth, 0);

      g.select('.y2.axis')
          .attr('transform', 'translate('+ x.range()[1] + ',0)');
      d3.transition(g.select('.y2.axis'))
          .call(y2Axis);
    });

    return chart;
  }

  chart.dispatch = dispatch;
  chart.legend = legend;
  chart.xAxis = xAxis;
  chart.yAxis = yAxis;

  d3.rebind(chart, lines, 'interactive');
  //consider rebinding x and y as well

  chart.x = function(_) {
    if (!arguments.length) return getX;
    getX = _;
    lines.x(_);
    return chart;
  };

  chart.y = function(_) {
    if (!arguments.length) return getY;
    getY = _;
    lines.y(_);
    return chart;
  };

  chart.margin = function(_) {
    if (!arguments.length) return margin;
    margin = _;
    return chart;
  };

  chart.width = function(_) {
    if (!arguments.length) return getWidth;
    getWidth = d3.functor(_);
    return chart;
  };

  chart.height = function(_) {
    if (!arguments.length) return getHeight;
    getHeight = d3.functor(_);
    return chart;
  };

  chart.dotRadius = function(_) {
    if (!arguments.length) return dotRadius;
    dotRadius = d3.functor(_);
    lines.dotRadius = _;
    return chart;
  };


  return chart;
}