docs/tutorial.html

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   3 <style>
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   8
   9 <p>To use dygraphs, include the <code><a href="download.html">dygraph-combined-dev.js</a></code> JavaScript file and instantiate a <code>Dygraph</code> object.</p>
  10
  11 <p>Here's a basic example to get things started:</p>
  12
  13 <div class="example" style="clear:both;">
  14   <div class="codeblock" style="float:left;width:400px;">
  15     <h3 style="text-align:center">HTML</h3>
  16   <pre>
  17 &lt;html&gt;
  18 &lt;head&gt;
  19 &lt;script type=&quot;text/javascript&quot;
  20   src=&quot;dygraph-combined-dev.js&quot;&gt;&lt;/script&gt;
  21 &lt;/head&gt;
  22 &lt;body&gt;
  23 &lt;div id=&quot;graphdiv&quot;&gt;&lt;/div&gt;
  24 &lt;script type=&quot;text/javascript&quot;&gt;
  25   g = new Dygraph(
  26
  27     // containing div
  28     document.getElementById(&quot;graphdiv&quot;),
  29
  30     // CSV or path to a CSV file.
  31     &quot;Date,Temperature\n&quot; +
  32     &quot;2008-05-07,75\n&quot; +
  33     &quot;2008-05-08,70\n&quot; +
  34     &quot;2008-05-09,80\n&quot;
  35
  36   );
  37 &lt;/script&gt;
  38 &lt;/body&gt;
  39 &lt;/html&gt;
  40 </pre>
  41   </div>
  42   <div class="codeoutput" style="float:left;">
  43     <h3 style="text-align:center">OUTPUT</h3>
  44     <div id="graphdiv"></div>
  45     <script type="text/javascript">
  46       g = new Dygraph(
  47
  48         // containing div
  49         document.getElementById("graphdiv"),
  50
  51         // CSV or path to a CSV file.
  52         "Date,Temperature\n" +
  53         "2008-05-07,75\n" +
  54         "2008-05-08,70\n" +
  55         "2008-05-09,80\n"
  56       );
  57     </script>
  58   </div>
  59 </div>
  60
  61 <p style="clear:both">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 its container to a reasonable default, calculates appropriate axis ranges and tick marks and draws the graph.</p>
  62
  63 <p>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 <code>"file:///"</code>. Here's an example: (data from <a href="http://www.wunderground.com/history/airport/KNUQ/2007/1/1/CustomHistory.html?dayend=31&amp;monthend=12&amp;yearend=2007&amp;req_city=NA&amp;req_state=NA&amp;req_statename=NA">Weather Underground</a>)</p>
  64
  65 <div class="example" style="clear:both;">
  66   <div class="codeblock" style="float:left;width:400px;">
  67     <h3 style="text-align:center">HTML</h3>
  68 <pre>
  69 &lt;html&gt;
  70 &lt;head&gt;
  71 &lt;script type=&quot;text/javascript&quot;
  72   src=&quot;dygraph-combined-dev.js&quot;&gt;&lt;/script&gt;
  73 &lt;/head&gt;
  74 &lt;body&gt;
  75 &lt;div id=&quot;graphdiv2&quot;
  76   style=&quot;width:500px; height:300px;&quot;&gt;&lt;/div&gt;
  77 &lt;script type=&quot;text/javascript&quot;&gt;
  78   g2 = new Dygraph(
  79     document.getElementById(&quot;graphdiv2&quot;),
  80     &quot;temperatures.csv&quot;, // path to CSV file
  81     {}          // options
  82   );
  83 &lt;/script&gt;
  84 &lt;/body&gt;
  85 &lt;/html&gt;
  86 </pre>
  87   </div>
  88   <div class="codeoutput" style="float:left;">
  89     <h3 style="text-align:center">OUTPUT</h3>
  90     <div id="graphdiv2" style="width:500px; height:300px;"></div>
  91     <script type="text/javascript">
  92       g2 = new Dygraph(
  93         document.getElementById("graphdiv2"),
  94         "temperatures.csv",
  95         {}
  96       );
  97     </script>
  98   </div>
  99 </div>
 100
 101 <p style="clear:both;">The file used is <code><a href="temperatures.csv">temperatures.csv</a></code>.</p>
 102
 103 <p>There are a few things to note here:</p>
 104
 105 <ul>
 106   <li>The Dygraph sent off an XHR to get the temperatures.csv file.</li>
 107   <li>The labels were taken from the first line of <code>temperatures.csv</code>, which is <code>Date,High,Low</code>.</li>
 108   <li>The Dygraph automatically chose two different, easily-distinguishable colors for the two data series.</li>
 109   <li>The labels on the x-axis have switched from days to months. If you zoom in, they'll switch to weeks and then days.</li>
 110   <li>Some heuristics are used to determine a good vertical range for the data. The idea is to make all the data visible and have human-friendly values on the axis (i.e. 200 instead of 193.4). Generally this works well.</li>
 111   <li>The data is very spiky. A moving average would be easier to interpret.</li>
 112 </ul>
 113
 114 <p>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 <code>rollPeriod</code> option. Here's how it's done:</p>
 115
 116 <div class="example" style="clear:both;">
 117   <div class="codeblock" style="float:left;width:400px;">
 118     <h3 style="text-align:center">HTML</h3>
 119 <pre>
 120 &lt;html&gt;
 121 &lt;head&gt;
 122 &lt;script type=&quot;text/javascript&quot;
 123   src=&quot;dygraph-combined-dev.js&quot;&gt;&lt;/script&gt;
 124 &lt;/head&gt;
 125 &lt;body&gt;
 126 &lt;div id=&quot;graphdiv3&quot;
 127   style=&quot;width:500px; height:300px;&quot;&gt;&lt;/div&gt;
 128 &lt;script type=&quot;text/javascript&quot;&gt;
 129   g3 = new Dygraph(
 130     document.getElementById(&quot;graphdiv3&quot;),
 131     &quot;temperatures.csv&quot;,
 132     {
 133       rollPeriod: 7,
 134       showRoller: true
 135     }
 136   );
 137 &lt;/script&gt;
 138 &lt;/body&gt;
 139 &lt;/html&gt;
 140 </pre>
 141   </div>
 142   <div class="codeoutput" style="float:left;">
 143     <h3 style="text-align:center">OUTPUT</h3>
 144     <div id="graphdiv3" style="width:500px; height:300px;"></div>
 145     <script type="text/javascript">
 146       g3 = new Dygraph(
 147         document.getElementById("graphdiv3"),
 148         "temperatures.csv",
 149         {
 150           rollPeriod: 7,
 151           showRoller: true
 152         }
 153       );
 154     </script>
 155   </div>
 156 </div>
 157
 158 <p style="clear:both;">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.</p>
 159
 160 <h2>Error Bars</h2>
 161
 162 <p>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 <em>&plusmn;n</em> 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. <em>&sigma; = sqrt( (&sigma;<sub>1<sup>2</sup></sub> + &sigma;<sub>2<sup>2</sup></sub> + ... + &sigma;<sub>n<sup>2</sup></sub>) / n )</em></p>
 163
 164 <p>Here's a demonstration. There are two data series. One is <code>N(100,10)</code> with a standard deviation of 10 specified at each point. The other is <code>N(80,20)</code> with a standard deviation of 20 specified at each point. The CSV file was generated using Octave and can be viewed at <a href="twonormals.csv">twonormals.csv</a>.</p>
 165
 166 <div class="example" style="clear:both;">
 167   <div class="codeblock" style="float:left;width:400px;">
 168     <h3 style="text-align:center">HTML</h3>
 169 <pre>
 170 &lt;html&gt;
 171 &lt;head&gt;
 172 &lt;script type=&quot;text/javascript&quot;
 173   src=&quot;combined.js&quot;&gt;&lt;/script&gt;
 174 &lt;/head&gt;
 175 &lt;body&gt;
 176 &lt;div id=&quot;graphdiv4&quot;
 177   style=&quot;width:480px; height:320px;&quot;&gt;&lt;/div&gt;
 178 &lt;script type=&quot;text/javascript&quot;&gt;
 179   g4 = new Dygraph(
 180     document.getElementById(&quot;graphdiv4&quot;),
 181     &quot;twonormals.csv&quot;,
 182     {
 183       rollPeriod: 7,
 184       showRoller: true,
 185       errorBars: true,
 186       valueRange: [50,125]
 187     }
 188   );
 189 &lt;/script&gt;
 190 &lt;/body&gt;
 191 &lt;/html&gt;
 192 </pre>
 193 </div>
 194 <div class="codeoutput" style="float:left;">
 195   <h3 style="text-align:center">OUTPUT</h3>
 196   <div id="graphdiv4" style="width:480px; height:320px;"></div>
 197   <script type="text/javascript">
 198     g4 = new Dygraph(
 199       document.getElementById("graphdiv4"),
 200       "twonormals.csv",
 201       {
 202         rollPeriod: 7,
 203         showRoller: true,
 204         errorBars: true,
 205         valueRange: [50,125]
 206       }
 207     );
 208   </script>
 209 </div>
 210 </div>
 211
 212 <p style="clear:both;">Things to note here:</p>
 213
 214 <ul>
 215 <li>The <strong>errorBars</strong> option affects both the interpretation of the CSV file and the display of the graph. When <strong>errorBars</strong> is set to true, each line is interpreted as <em>YYYYMMDD</em>, <em>A</em>, <em>sigma_A</em>, <em>B</em>, <em>sigma_B</em>, &hellip;</li>
 216 <li>The first line of the CSV file doesn't mention the error columns. In this case, it's just "Date,Series1,Series2".</li>
 217 <li>The averaging visibly affects the error bars. This is most clear if you crank up the rolling period to something like 100 days. For the earliest dates, there won't be 100 data points to average so the signal will be noisier. The error bars get smaller like sqrt(N) going forward in time until there's a full 100 points to average.</li>
 218 <li>The error bars are partially transparent. This can be seen when they overlap one another.</li>
 219 </ul>
 220
 221
 222 <h2 id="gviz">GViz Data</h2>
 223
 224 <p>The <a
 225   href="http://code.google.com/apis/visualization/documentation/index.html">Google
 226   Visualization API</a> provides a standard interface for describing data.
 227 Once you've specified your data using this API, you can plug in any
 228 GViz-compatible visualization. dygraphs is such a visualization. In
 229 particular, it can be used as a drop-in replacement for the
 230 AnnotatedTimeline visualization used on Google Finance and other sites. To
 231 see how this works, check out the <a href="tests/annotation-gviz.html">gviz
 232   annotation demo.</a></p>
 233
 234 <p>Here is another demonstration of
 235 <a href="http://danvk.org/dygraphs/tests/gviz.html">how to use dygraphs a GViz visualization</a>.
 236 </p>
 237
 238 <h2 id="baseball">Charting Fractions</h2>
 239
 240 <p>Situations often arise where you want to plot fractions, e.g. the fraction of respondents in a poll who said they'd vote for candidate X or the number of hits divided by at bats (baseball's batting average). Fractions require special treatment for two main reasons:</p>
 241
 242 <ul>
 243   <li>The average of <code>a1/b1</code> and <code>a2/b2</code> is <code>(a1+a2)/(b1+b2)</code>, not <code>(a1/b1 + a2/b2)/2</code>.</li>
 244   <li>The normal approximation is not always applicable and more sophisticated confidence intervals (e.g. the <a href="http://en.wikipedia.org/wiki/Binomial_proportion_confidence_interval">Wilson confidence interval</a>) must be employed to avoid ratios that exceed 100% or go below 0%.</li>
 245 </ul>
 246
 247 <p>Fortunately, dygraphs handles both of these for you! Here's a chart and the command that generated it:</p>
 248
 249 <div style="width:750px; text-align:center; font-weight: bold; font-size: 125%;">Batting Average for Ichiro Suzuki vs. Mariners (2004)</div>
 250 <div id="baseballdiv" style="width:750px; height:300px;"></div>
 251 <script type="text/javascript">
 252   new Dygraph(
 253     document.getElementById("baseballdiv"),
 254     "suzuki-mariners.txt",
 255     {
 256       fractions: true,
 257       errorBars: true,
 258       showRoller: true,
 259       rollPeriod: 15
 260     }
 261   );
 262 </script>
 263
 264 <b>Code:</b>
 265 <pre>
 266 new Dygraph(
 267   document.getElementById(&quot;baseballdiv&quot;),
 268   &quot;suzuki-mariners.txt&quot;,
 269   {
 270     fractions: true,
 271     errorBars: true,
 272     showRoller: true,
 273     rollPeriod: 15
 274   }
 275 );
 276 </pre>
 277
 278 <p>The <code>fractions</code> option indicates that the values in each column should be parsed as fractions (e.g. "1/2" instead of "0.5"). The <code>errorBars</code> option indicates that we'd like to see a confidence interval around each data point. By default, when <code>fractions</code> is set, you get a Wilson confidence interval. If you look carefully at the chart, you can see that the error bars are asymmetric.</p>
 279
 280 <p>A couple things to notice about this chart:</p>
 281
 282 <ul>
 283   <li>The error bars for Ichiro's batting average are larger than for the Mariners', since he has far fewer at bats than his team.</li>
 284   <li>dygraphs makes it easy to see "batting average over the last 30 games". This is ordinarily quite difficult to compute. It makes it clear where the "hot" and "cold" part of Suzuki's season were.</li>
 285   <li>If you set the averaging period to something large, like 200, you'll see the team's and player's batting average through that game. The final number is the overall batting average for the season.</li>
 286   <li>Where the error bars do not overlap, we can say with 95% confidence that the series differ. There is a better than 95% chance that Ichiro was a better hitter than his team as a whole in 2004, the year he won the batting title.</li>
 287 </ul>
 288
 289 <h2 id="stock">One last demo</h2>
 290
 291 <p>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.</p>
 292
 293 <div id="dow_chart" style="width:750px; height:350px;"></div>
 294 <p><b>Display: </b>
 295 <input type=checkbox id=0 onClick="stockchange(this)" checked>
 296 <label for="0"> Nominal</label>
 297 <input type=checkbox id=1 onClick="stockchange(this)" checked>
 298 <label for="1"> Real</label>
 299 <input type=checkbox id=ann onClick="annotationschange(this)" checked>
 300 <label for="ann"> Annotations</label>
 301 </p>
 302
 303 <script type="text/javascript">
 304   var stock_annotations = [
 305     {
 306       series: "Real",
 307       x: "1929-08-15",
 308       shortText: "A",
 309       text: "1929 Stock Market Peak",
 310       cssClass: 'annotation'
 311     },
 312     {
 313       series: "Nominal",
 314       x: "1987-08-15",
 315       shortText: "B",
 316       text: "1987 Crash",
 317       cssClass: 'annotation'
 318     },
 319     {
 320       series: "Nominal",
 321       x: "1999-12-15",
 322       shortText: "C",
 323       text: "1999 (.com) Peak",
 324       cssClass: 'annotation'
 325     },
 326     {
 327       series: "Nominal",
 328       x: "2007-10-15",
 329       shortText: "D",
 330       text: "All-Time Market Peak",
 331       cssClass: 'annotation'
 332     }
 333   ];
 334
 335 // From http://www.econstats.com/eqty/eq_d_mi_3.csv
 336   stockchart = new Dygraph(
 337     document.getElementById('dow_chart'),
 338     "dow.txt",
 339     {
 340       showRoller: true,
 341       customBars: true,
 342       labelsKMB: true,
 343       drawCallback: function(g, is_initial) {
 344         if (!is_initial) return;
 345         g.setAnnotations( stock_annotations );
 346       }
 347     }
 348   );
 349
 350   function stockchange(el) {
 351     stockchart.setVisibility(el.id, el.checked);
 352   }
 353
 354   function annotationschange(el) {
 355     if (el.checked) {
 356       stockchart.setAnnotations(stock_annotations);
 357     } else {
 358       stockchart.setAnnotations([]);
 359     }
 360   }
 361 </script>
 362 <!--
 363
 364 Here is a script to regenerate the Dow Jones plot:
 365
 366 # Get unadjusted DJIA data in a nice format:
 367 curl -O http://www.econstats.com/eqty/eq_d_mi_3.csv
 368 sed '1,17d' eq_d_mi_3.csv | cut -d, -f1,6 | perl -pe 's/(\d{4}-\d\d)-\d\d/$1/g' | perl -pe 's/, */\t/' | grep -v 'na' | perl -ne 'chomp; ($m,$v) = split/\t/; $close{$m} = $v; if ($low{$m} == 0 || $v < $low{$m}) { $low{$m}=$v } if ($v > $high{$m}) { $high{$m} = $v } END { for $x(sort keys %close) { print "$x\t$low{$x}\t$close{$x}\t$high{$x}\n" } } ' > monthly-djia.tsv
 369
 370 # Fetch and format the CPI data:
 371 curl 'http://data.bls.gov/PDQ/servlet/SurveyOutputServlet?series_id=CUUR0000SA0&years_option=all_years&periods_option=all_periods&output_type=column&output_format=text&delimiter=comma' > cpi-u.txt
 372 sed '1,/Series Id,Year,/d' cpi-u.txt | sed '/^$/,$d' | cut -d, -f2,3,4 | perl -ne 'print if /,M(0[0-9]|1[012]),/' | perl -pe 's/(\d{4}),M(\d{2}),/$1-$2\t/g' > cpi-u.tsv
 373
 374 # Merge:
 375 join -t'     ' cpi-u.tsv monthly-djia.tsv > annotated-djia.tsv
 376 perl -ne 'BEGIN{print "Month,Nominal,Real\n"} chomp; ($m,$cpi,$low,$close,$high) = split /\t/; $cpi /= 100.0; print "$m-15,$low;$close;$high,",($low/$cpi),";",($close/$cpi),";",($high/$cpi),"\n"' annotated-djia.tsv > dow.txt
 377
 378 -->
 379
 380 <h2>Common Gotchas</h2>
 381
 382 <p>Here are a few problems that I've frequently run into while using the dygraphs library.</p>
 383
 384 <ul>
 385   <li>If your chart doesn't display, be sure to check your browser's JavaScript error console. dygraphs makes every attempt to log errors and warnings, and these can often guide you in the right direction.</li>
 386   <li>Make sure your CSV files are readable! If your graph isn't showing up, the XMLHttpRequest for the CSV file may be failing. You can determine whether this is the case using tools like <a href="http://www.getfirebug.com/">Firebug</a>.</li>
 387   <li>Make sure your CSV files are in the correct format. They must be of the form <code>YYYYMMDD, series1, series2, </code>&hellip; . And if you set the <code>errorBars</code> property, make sure you alternate data series and standard deviations.</li>
 388   <li>dygraphs are not happy when placed inside a <code>&lt;center&gt;</code> tag. This applies to the CSS <code>text-align</code> property as well. If you want to center a Dygraph, put it inside a table with <code>align = center</code> set.</li>
 389   <li>Don't set the <code>dateWindow</code> property to a date. It expects milliseconds since epoch, which can be obtained from a JavaScript Date object's valueOf method.</li>
 390   <li>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.</li>
 391 </ul>
 392
 393 <h2>What next?</h2>
 394
 395 <p>If you need to support Internet Explorer, check out our <a href="ie.html">notes on IE</a>.</p>
 396
 397 <p>To get some inspiration, look at how the <a href="gallery/">charts in our gallery</a> are built.</p>
 398
 399
 400 <!--#include virtual="footer.html" -->