title: Animate lines in a line graph with D3.js
body: <p>I have my line graph, with 2 lines.
  Data to draw my line graph is pulled from a .csv file.</p>
  
  <p>Can anyone explain how I could start off with an empty graph, and when I click a button, 
  my lines animate across the graph?</p>
  
  <p>Thanks in advance!!</p>
  
  <p>
      var button=d3.select("#button");</p>
  
  <pre><code>var margin = {top: 30, right: 20, bottom: 50, left: 60},
  width = 700 - margin.left - margin.right,
  height = 300 - margin.top - margin.bottom;
  
  var parseDate = d3.time.format("%d-%b-%y").parse;
  
  
  //treats value passed to it as a time/date
  //OUTPUT RANGE
  var x = d3.time.scale()
      .range([0, width]);
  
  //OUTPUT RANGE  
  var y = d3.scale.linear()
      .range([height, 0]);
  
  var xAxis = d3.svg.axis().scale(x)
      .orient("bottom")
      .ticks(5);
  
  var yAxis = d3.svg.axis().scale(y)
      .orient("left")
      .ticks(5);
  
  //assigns coordinates for each piece of data    
  var valueline = d3.svg.line()
      .interpolate("linear")
      .x(function(d) { return x(d.date); })
      .y(function(d) { return y(d.close); });
  
  //second line data
  var valueline2 = d3.svg.line()
      .x(function(d) { return x(d.date); })
      .y(function(d) { return y(d.open); });
  
  //create area for 'area' below line 
  var area = d3.svg.area()
      .x(function(d) { return x(d.date); })
      .y0(height)
      .y1(function(d) { return y(d.close); });    
  
  //creates area to draw graph    
  var svg = d3.select("body")
      .append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
  //groups content    
  .append("g")
      .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
  
  function make_x_axis() {
      return d3.svg.axis()
          .scale(x)
          .orient("bottom")
          .ticks(5)
  }
  
  function make_y_axis() {
      return d3.svg.axis()
          .scale(y)
          .orient("left")
          .ticks(30)
  }
  
  // csv callback function
  d3.csv("myData2.csv", function(data) {
      data.forEach(function(d) {
      d.date = parseDate(d.date);
      //+ operator sets any 'close' values to nuneric
      d.close = +d.close;
      d.open = +d.open;   
  </code></pre>
  
  <p>});</p>
  
  <pre><code>//INPUT DOMAINS
  //.extent() returns min and max values of argument
  x.domain(d3.extent(data, function(d) { return d.date; }));
  //returns max of whichever set of data is bigger
  y.domain([0, d3.max(data, function(d) { return Math.max(d.close, d.open); })]);
  
  //draws lines
  //passes the valueline array to path object
  svg.append("path") // Add the valueline path.
      .attr("class", "line")
      //adds dashed line
      .style("stroke-dasharray", ("5, 9")) // &lt;== This line here!!
      .attr("d", valueline(data));
  
  
  button.on("click", function() { 
      svg.append("path")      // Add the valueline2 path. 
          .attr("class", "line2")
          .transition()
          .attr("d", valueline2(data));
      })
  
  
  svg.append("g") // Add the X Axis
      .attr("class", "x axis")
      //moves x axis to bottom of graph
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis);
  
  //text label for x-axis 
  svg.append("text") // text label for the x axis
      .attr("transform", "translate(" + (width / 2) + " ," + (height + margin.bottom - 5 ) + ")")
      .style("text-anchor", "middle")
      .text("Date");
  
  svg.append("g") // Add the Y Axis
      .attr("class", "y axis")
      .call(yAxis);
  
  //text label for y-axis 
  svg.append("text")
      .attr("transform", "rotate(-90)")
      .attr("y", 0 - margin.left)
      .attr("x",0 - (height / 2))
      //adds extra left padding as original y pos = 0
      .attr("dy", "1em")
      .style("text-anchor", "middle")
      .text("Value");
  
  
  //adding a title to the graph
  svg.append("text")
      .attr("x", (width / 2))
      .attr("y", 0 - (margin.top / 2))
      .attr("text-anchor", "middle")
      .style("font-size", "16px")
      .style("text-decoration", "underline")
      .text("Me Graph Larry");
  
  
  //draw x axis grid  
  svg.append("g")
      .attr("class", "grid")
      .attr("transform", "translate(0," + height + ")")
      .call(make_x_axis()
      .tickSize(-height, 0, 0)
      .tickFormat("")
  )
  
  //draw y axis grid
  svg.append("g")
      .attr("class", "grid")
      .call(make_y_axis()
      .tickSize(-width, 0, 0)
      .tickFormat("")
  )
  
  });&lt;!--d3.csv close--&gt;
  </code></pre>
  
  <p></p>