dygraphs JavaScript Library
code.google.com/p/dygraphs

The dygraphs JavaScript library produces produces interactive, zoomable charts of time series based on CSV files.

Features

Caveats

Demo

(Mouse over to highlight individual values. Click and drag to zoom. Double-click to zoom out.)

Usage

The DateGraph library depends on two other JS libraries: MochiKit and PlotKit. Rather than tracking down copies of these libraries, I recommend using a packed version of dygraphs that combines all three libraries into a single JS file. Either grab this file from dygraph project's downloads page or create it yourself by checking out a copy of the code and running: 

./generate-combined.sh

The combined JS file is now in dygraph-combined.js. Here's a basic example to get things started:

HTML Output
<html>
<head>
<script type="text/javascript" src="combined.js"></script>
</head>
<body>
<div id="graphdiv" style="width:400px; height:300px;"></div>
<script type="text/javascript">
  g = new DateGraph(
        document.getElementById("graphdiv"),  // containing div
        function() {                // function or path to CSV file.
          return "20080507,75\n" +
                 "20080508,70\n" +
                 "20080509,80\n";
        },
        [ "Temperature" ],          // names of data series
        {}                          // additional options (see below)
      );
</script>
</body>
</html>

In order to keep this example self-contained, the second parameter is a function that returns CSV data. These lines must begin with a date in the form YYYYMMDD. In most applications, it makes more sense to include a CSV file instead. If the second parameter to the constructor is a string, it will be interpreted as the path to a CSV file. The DateGraph will perform an XMLHttpRequest to retrieve this file and display the data when it becomes available. Make sure your CSV file is readable and serving from a place that understands XMLHttpRequest's! In particular, you cannot specify a CSV file using "file:///". Here's an example: (data from Weather Underground)

HTML Output
<html>
<head>
<script type="text/javascript" src="combined.js"></script>
</head>
<body>
<div id="graphdiv" style="width:600px; height:300px;"></div>
<script type="text/javascript">
  g = new DateGraph(
        document.getElementById("graphdiv"),
        "temperatures.csv",  // path to CSV file
        null,                // labels in top line of CSV file
        {}
      );
</script>
</body>
</html>

Click here to view the temperatures.csv file. There are a few things to note here:

These last two problems can be fixed by specifying the appropriate options in the fourth parameter to the DateGraph constructor. To set the number of days for a moving average, use the rollPeriod option. To set the range of the y-axis, use the valueRange option. Here's how it's done:

HTML Output
<html>
<head>
<script type="text/javascript" src="combined.js"></script>
</head>
<body>
<div id="graphdiv" style="width:600px; height:300px;"></div>
<script type="text/javascript">
  g = new DateGraph(
        document.getElementById("graphdiv"),
        "temperatures.csv", null,
        { rollPeriod: 7,
          showRoller: true,
          valueRange: [25, 100]
        }
      );
</script>
</body>
</html>

A rolling average can be set using the text box in the lower left-hand corner of the graph (the showRoller attribute is what makes this appear).

Error Bars

Another significant feature of the dygraphs library is the ability to display error bars around data series. One standard deviation must be specified for each data point. A +/-n sigma band will be drawn around the data series at that point. If a moving average is being displayed, DateGraph will compute the standard deviation of the average at each point. (i.e. σ = sqrt((σ_1^2 + σ_2^2 + ... + σ_n^2)/n))

Here's a demonstration. There are two data series. One is N(100,10) with a standard deviation of 10 specified at each point. The other is N(80,20) with a standard deviation of 20 specified at each point. The CSV file was generated using Octave and can be viewed here.

HTML Output
<html>
<head>
<script type="text/javascript"
  src="combined.js"></script>
</head>
<body>
<div id="graphdiv" 
 style="width:800px; height:400px;"
 ></div>
<script type="text/javascript">
$ = document.getElementById;
g = new DateGraph(
  $("graphdiv"),
  "twonormals.csv",
  null,
  { rollPeriod: 7,
    showRoller: true,
    errorBars: true,
    valueRange: [50,125]
  }
);
</script>
</body>
</html>

Things to note here:

One last demo

This chart shows monthly closes of the Dow Jones Industrial Average, both in nominal and real (i.e. adjusted for inflation) dollars. The shaded areas show its monthly high and low. CPI values with a base from 1982-84 are used to adjust for inflation.

Other Options

These are the options that can be passed in through the fourth parameter of the DateGraph constructor.

NameSample ValueDescription
rollPeriod 7 Number of days over which to average data. Discussed extensively above.
showRoller true Should the rolling average period text box be shown? Default is false.
colors ['red', '#00FF00'] List of colors for the data series. These can be of the form "#AABBCC" or "rgb(255,100,200)" or "yellow", etc. If not specified, equally-spaced points around a color wheel are used.
colorSaturation 1.0 If colors is not specified, saturation of the automatically-generated data series colors. (0.0-1.0, default: 1.0)
colorValue 0.5 If colors is not specified, value of the data series colors, as in hue/saturation/value. (0.0-1.0, default 0.5)
clickCallback function(e,date){ alert(date); } A function to call when a data point is clicked. The function should take two arguments, the event object for the click and the date that was clicked. (default null)
errorBars false Does the data contain standard deviations? Setting this to true alters the input format (see above). (default false)
strokeWidth 2.0 Width of the data lines. This can be used to increase the contrast or some graphs. (default 1.0)
dateWindow [(new Date('2006-01-01')).valueOf(),
(new Date()).valueOf()]		 Initially zoom in on a section of the graph. Is of the form [earliest, latest], where earliest/latest are millis since epoch. By default, the full range of the input is shown.
valueRange [10, 110] Explicitly set the vertical range of the graph to [low, high]. By default, some clever heuristics are used (see above).
minTickSize 1 The difference between ticks on the y-axis can be greater than or equal to this, but no less. If you set it to 1, for instance, you'll never get nonintegral gaps between ticks.
labelsSeparateLines true Put <br/> between lines in the label string. Often used in conjunction with labelsDiv. (default false)
labelsDiv document.getElementById('foo') Show data labels in an external div, rather than on the graph. (default null)
labelsKMB true Show K/M/B for thousands/millions/billions on y-axis (default false).
padding {left: 40, right: 30,
top: 5, bottom: 15}		 Adds extra pixels of padding around the graph. Sometimes a dygraph gets clipped by surrounding text (see the Demo at the top of this page). Setting this property appropriately will fix this problem.

Any options you specify also get passed on to PlotKit's Renderer class. DateGraph will override some of these (e.g. strokeColor), but others may be useful. The padding property is an example of this.

Common Gotchas

Here are a few problems that I've frequently run into while using the dygraphs library.

Created May 9, 2008 by Dan Vanderkam