dygraphs JavaScript Library

The dygraphs JavaScript library produces produces interactive, zoomable charts of time series.

dygraphs JavaScript Visualization Library
+http://github.com/danvk/dygraphs
+See gallery and open issues

+ +

The dygraphs JavaScript library produces produces interactive, zoomable charts of time series. It is designed to display dense data sets and enable users to explore and interpret them.

Features

Plots time series without using an external server or Flash
Supports multiple data series
Supports error bands around data series
Displays values on mouseover
Displays values on mouseover (this makes it easily discoverable)
Interactive zoom
Adjustable averaging period
Customizable click-through actions
Compatible with the Google Visualization API
Works in Internet Explorer (using excanvas)
Intelligent defaults make it easy to use
Lightweight (45kb) and responsive

Caveats

Requires Firefox 1.5+ or Safari/WebKit 1.3+.
Internet Explorer is poorly supported.

- -

Demo

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

Demo

(Mouse over to highlight individual values. Click and drag to zoom. Double-click to zoom back out. Change the number and hit enter to adjust the averaging period.)

Temperatures in New York vs. San Francisco

For more demos, browse the dygraph tests directory.

Some things to notice:

There's less seasonal temperature variation in SF than in NY. +
The difference is about 15° F for SF vs. 50° F for NY. +
The daily data (set rolling period to 1) is quite noisy and hides this conclusion. +
Using a 14-day moving average makes it clearer. A 100-day rolling period averages out nearly all the specifics from the data. +
There's a gap in the data for SF, when the weather station was down (zoom into October 2007 to see it). +
The bands around each point indicate average highs and lows. +
There is a lot of data in this chart: low, average and high for each city on each day of a three year period ≈ 6000 data points in all. +

Usage

For more demos, browse the dygraph tests directory.

The dygraphs 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: +

Usage

./generate-combined.sh

To use dygraphs, include the dygraph-combined.js JavaScript file and instantiate a Dygraph object.

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

Here's a basic example to get things started:

@@ -104,17 +168,20 @@

HTML	<html> <head> -<script type="text/javascript" src="combined.js"></script> +<script type="text/javascript" + src="dygraph-combined.js"></script> </head> <body> <div id="graphdiv"></div> <script type="text/javascript"> g = new Dygraph( - document.getElementById("graphdiv"), // containing div - "Date,Temperature\n" + // CSV or path to a CSV file. - "20080507,75\n" + - "20080508,70\n" + - "20080509,80\n", + // containing div + document.getElementById("graphdiv"), + // CSV or path to a CSV file. + "Date,Temperature\n" + + "2008-05-07,75\n" + + "2008-05-08,70\n" + + "2008-05-09,80\n" ); </script> </body> @@ -122,18 +189,21 @@	-

HTML

 <html>
 <head>
-<script type="text/javascript" src="combined.js"></script>
+<script type="text/javascript"
+  src="dygraph-combined.js"></script>
 </head>
 <body>
 <div id="graphdiv"></div>
 <script type="text/javascript">
   g = new Dygraph(
-        document.getElementById("graphdiv"),  // containing div
-        "Date,Temperature\n" +                // CSV or path to a CSV file.
-        "20080507,75\n" +
-        "20080508,70\n" +
-        "20080509,80\n",
+        // containing div
+        document.getElementById("graphdiv"),
+        // CSV or path to a CSV file.
+        "Date,Temperature\n" +
+        "2008-05-07,75\n" +
+        "2008-05-08,70\n" +
+        "2008-05-09,80\n"
       );
 </script>
 </body>
@@ -122,18 +189,21 @@

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 Dygraph 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)

+ + +

In order to keep this example self-contained, the second parameter is raw CSV data. The dygraphs library parses this data (including column headers), resizes the its container to a reasonable default, calculates appropriate axis ranges and tick marks and draws the graph.

+ +

In most applications, it makes more sense to include a CSV file instead. If the second parameter to the constructor doesn't contain a newline, it will be interpreted as the path to a CSV file. The Dygraph 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)

@@ -143,30 +213,33 @@

HTML	<html> <head> -<script type="text/javascript" src="combined.js"></script> +<script type="text/javascript" + src="dygraph-combined.js"></script> </head> <body> -<div id="graphdiv" style="width:600px; height:300px;"></div> +<div id="graphdiv" + style="width:500px; height:300px;"></div> <script type="text/javascript"> - g = new Dygraph( - document.getElementById("graphdiv"), - "temperatures.csv", // path to CSV file - {} // additional options - ); + new Dygraph( + document.getElementById("graphdiv"), + "temperatures.csv", // path to CSV file + {} // options + ); </script> </body> </html>	- - +

HTML

 <html>
 <head>
-<script type="text/javascript" src="combined.js"></script>
+<script type="text/javascript"
+  src="dygraph-combined.js"></script>
 </head>
 <body>
-<div id="graphdiv" style="width:600px; height:300px;"></div>
+<div id="graphdiv"
+  style="width:500px; height:300px;"></div>
 <script type="text/javascript">
-  g = new Dygraph(
-        document.getElementById("graphdiv"),
-        "temperatures.csv",  // path to CSV file
-        {}                   // additional options
-      );
+  new Dygraph(
+    document.getElementById("graphdiv"),
+    "temperatures.csv",  // path to CSV file
+    {}                   // options
+  );
 </script>
 </body>
 </html>

- +

+ +

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

The data is very spiky. A moving average would be easier to interpret.

This problem can be fixed by specifying the appropriate options in the "additional options" parameter to the Dygraph constructor. To set the number of days for a moving average, use the rollPeriod option. Here's how it's done:

@@ -188,10 +261,12 @@

HTML	<html> <head> -<script type="text/javascript" src="combined.js"></script> +<script type="text/javascript" + src="dygraph-combined.js"></script> </head> <body> -<div id="graphdiv" style="width:600px; height:300px;"></div> +<div id="graphdiv" + style="width:500px; height:300px;"></div> <script type="text/javascript"> g = new Dygraph( document.getElementById("graphdiv"), @@ -205,19 +280,18 @@ </html>	- - +

HTML

 <html>
 <head>
-<script type="text/javascript" src="combined.js"></script>
+<script type="text/javascript"
+  src="dygraph-combined.js"></script>
 </head>
 <body>
-<div id="graphdiv" style="width:600px; height:300px;"></div>
+<div id="graphdiv"
+  style="width:500px; height:300px;"></div>
 <script type="text/javascript">
   g = new Dygraph(
         document.getElementById("graphdiv"),
@@ -205,19 +280,18 @@
 </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).

+ + +

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). Also note that we've explicitly set the size of the chart div.

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, dygraphs 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))

@@ -237,7 +311,7 @@ </head> <body> <div id="graphdiv" - style="width:800px; height:400px;" + style="width:600px; height:300px;" ></div> <script type="text/javascript"> $ = document.getElementById; @@ -255,8 +329,10 @@ g = new Dygraph( </html> -

- - +

Things to note here:

The error bars are partially transparent. This can be seen when they overlap one another.

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 optional third parameter of the Dygraph constructor. To see demonstrations of many of these options, browse the dygraphs tests directory.

- +

+ + + + + + @@ -426,7 +509,7 @@ perl -ne 'BEGIN{print "Month,Nominal,Real\n"} chomp; ($m,$cpi,$low,$close,$high) - + @@ -434,6 +517,23 @@ perl -ne 'BEGIN{print "Month,Nominal,Real\n"} chomp; ($m,$cpi,$low,$close,$high) + + + + + + + + + + + +

Name	Sample Value	Description
includeZero	`true, false`	Usually, dygraphs will use the range of the data plus some padding to + set the range of the y-axis. If this option is set, the y-axis will always + include zero, typically as the lowest value. This can be used to avoid + exaggerating the variance in the data.
rollPeriod	`7`	Number of days over which to average data. Discussed extensively above.	Additional styles to apply to the currently-highlighted points div. For example, { 'font-weigth': 'bold' } will make the labels bold.
highlightCircleSize	`3`
drawPoints	`false`	Draw a small dot at each point, in addition to a line going through + the point. This makes the individual data points easier to see, but can + increase visual clutter in the chart. Default: false
pointSize	`1.0`	The size of the dot to draw on each point in pixels (see + drawPoints). A dot is always drawn when a point is "isolated", i.e. + there is a missing point on either side of it. This also controls the + size of those dots.
pixelsPerXLabel, pixelsPerYLabel	50	Number of pixels to require between each x- and y-label. Larger values @@ -501,8 +601,6 @@ perl -ne 'BEGIN{print "Month,Nominal,Real\n"} chomp; ($m,$cpi,$low,$close,$high)

Any options you specify also get passed on to PlotKit's Renderer class. dygraphs 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.

@@ -526,13 +624,29 @@ dygraphs library.

Don't set the dateWindow property to a date. It expects milliseconds since epoch, which can be obtained from a JavaScript Date object's valueOf method.

+ +

Make sure you don't have any trailing commas in your call to the Dygraph + constructor or in the options parameter. Firefox, Chrome and Safari ignore + these but they can cause a graph to not display in Internet Explorer.

Data Policy

dygraphs is purely client-side JavaScript. It does not send your data to any servers -- the data is processed entirely in the client's browser.

Created May 9, 2008 by Dan Vanderkam