docs/data.html

   1 <html>
   2   <head>
   3     <title>dygraphs input types</title>
   4     <style type="text/css">
   5       code { white-space: pre; border: 1px dashed black; display: block; }
   6       pre  { white-space: pre; border: 1px dashed black; }
   7       body { max-width: 800px; }
   8     </style>
   9   </head>
  10   <body>
  11     <h2>dygraphs Data Format</h2>
  12
  13     <p>When you create a Dygraph object, your code looks something like
  14     this:</p>
  15
  16     <code>
  17       g = new Dygraph(document.getElementById("div"),
  18                       <i>data</i>,
  19                       { <i>options</i> });
  20     </code>
  21
  22     <p>This document is about what you can put in the <i>data</i>
  23     parameter.</p>
  24
  25     <p>There are five types of input that dygraphs will accept:</p>
  26     <ol>
  27       <li><a href="#csv">CSV data</a>
  28       <li><a href="#url">URL</a>
  29       <li><a href="#array">array (native format)</a>
  30       <li><a href="#function">function</a>
  31       <li><a href="#datatable">DataTable</a>
  32     </ol>
  33
  34     <p>These are all discussed below. If you're trying to debug why your input
  35     won't parse, <b>check the JS error console</b>. dygraphs tries to log
  36     informative errors explaining what's wrong with your data, and these can
  37     often point you in the right direction.</p>
  38
  39     <p>There are several options which affect how your input data is
  40     interpreted. These are:
  41     <ul>
  42       <li> <i>xValueParser</i> affects CSV only.
  43       <li> <i>errorBars</i> affects all input types.
  44       <li> <i>customBars</i> affects all input types.
  45       <li> <i>fractions</i> affects all input types.
  46       <li> <i>labels</i> affects all input types.
  47     </ul>
  48     </p>
  49
  50     <a name="csv"><h3>CSV</h3>
  51     <p>Here's an example of what CSV data should look like:</p>
  52     <pre>
  53     Date,Series1,Series2
  54     2009/07/12,100,200  # comments are OK on data lines
  55     2009/07/19,150,201
  56     </pre>
  57
  58     <p>"CSV" is actually a bit of a misnomer: the data can be tab-delimited,
  59     too. The delimiter is set by the <i>delimiter</i> option. It default to ",".
  60     If no delimiter is found in the first row, it switches over to tab.</p>
  61
  62     <p>CSV parsing can be split into three parts: headers, x-value and
  63     y-values.</p>
  64
  65     <h4>Headers</h4>
  66     <p>If you don't specify the <i>labels</i> option, dygraphs will look at the
  67     first line of your CSV data to get the labels. If you see numbers for series
  68     labels when you hover over the dygraph, it's likely because your first line
  69     contains data but is being parsed as a label. The solution is to either add
  70     a header line or specify the labels like this:</p>
  71
  72     <code>
  73       new Dygraph(el,
  74                   "2009/07/12,100,200\n" +
  75                   "2009/07/19,150,201\n",
  76                   { labels: [ "Date", "Series1", "Series2" ] });
  77     </code>
  78
  79     <h4>x-values</h4>
  80     <p>Once the headers are parsed, dygraphs needs to determine what the type of
  81     the x values is. They're either dates or numbers. To make this
  82     determination, it looks at the first column of the first row ("2009/07/12"
  83     in the example above). Here's the heuristic: if it contains a '-' or a '/',
  84     or otherwise doesn't parse as a float, the it's a date. Otherwise, it's a
  85     number.</p>
  86
  87     <p>Once the type is determined, that doesn't mean all the values will parse
  88     correctly. The general rule is:<p>
  89
  90     <ul>
  91       <li>For dates, your strings have to be parseable by <i>Date.parse</i>.
  92       <li>For numbers, your strings have to be parseable by <i>parseFloat</i>.
  93     </ul>
  94
  95     <p>You can manually verify this using a JavaScript console. If a value
  96     doesn't parse, dygraphs will put a warning about it on your console. But
  97     beware: different browsers support different date formats!</p>
  98
  99     <p>Here are some valid date formats:</p>
 100     <ul>
 101       <li>2009-07-12</li>
 102       <li>2009/07/12</li>
 103       <li>2009/07/12 12</li>
 104       <li>2009/07/12 12:34</li>
 105       <li>2009/07/12 12:34:56</li>
 106     </ul>
 107
 108     <p>If you specify the <i>xValueParser</i> option, then all this detection is
 109     bypassed and your function is called instead. Your parser function takes in
 110     a string and needs to return a number. For dates/times, you should return
 111     milliseconds since epoch. You may also want to specify a few other options
 112     to make sure that everything gets displayed properly.<p>
 113
 114     <p>Here's code which parses a CSV file with unix timestamps in the first
 115     column:</p>
 116
 117     <code>
 118       new Dygraph(el,
 119                   "Date,Series1,Series2\n" +
 120                   "1247382000,100,200\n" +
 121                   "1247986800,150,201\n",
 122                   {
 123                     xValueFormatter: Dygraph.dateString_,
 124                     xValueParser: function(x) { return 1000*parseInt(x); },
 125                     xTicker: Dygraph.dateTicker
 126                   });
 127     </code>
 128
 129     <h4>y-values</h4>
 130     <p>Dependent (y-axis) values are simpler than x-values because they're
 131     always numbers. The complexity here comes from the various ways that you can
 132     specify the uncertainty in your measurements.<p>
 133
 134     <p>If your y-values are just numbers, then they need to be parseable by
 135     JavaScript's parseFloat function. Acceptable formats include:</p>
 136
 137     <ul>
 138       <li>12
 139       <li>-12
 140       <li>12.
 141       <li>12.3
 142       <li>1.24e+1
 143       <li>-1.24e+1
 144     </ul>
 145
 146     <p>If you have missing data, just leave the column blank (your CSV file will
 147     probably contain a ",," in it).</p>
 148
 149     <p>If your numbers have uncertainty associated with them, then there are
 150     three basic ways to express this: using fractions, standard deviations or
 151     explicit ranges.</p>
 152
 153     <h5>Fractions</h5>
 154     <p>If you specify the <i>fractions</i> option, then your data will all be
 155     interpreted as ratios between zero and one. This is often the case if you're
 156     plotting a percentage.</p>
 157
 158     <code>
 159       new Dygraph(el,
 160                   "X,Frac1,Frac2\n" +
 161                   "1,1/2,3/4\n"+
 162                   "2,1/3,2/3\n"+
 163                   "3,2/3,17/49\n"+
 164                   "4,25/30,100/200",
 165                   { fractions: true });
 166     </code>
 167
 168     <p>Why not just divide the fractions out yourself? There are two attractive
 169     reasons not to:</p>
 170
 171     <ul>
 172       <li>If you set both <i>fractions</i> and <i>errorBars</i>, then the
 173     denominator is interpreted as a sample size and dygraphs will plot <a
 174       href="http://en.wikipedia.org/wiki/Binomial_proportion_confidence_interval">Wilson
 175       binomial proportion confidence intervals</a> around each point.
 176
 177       <li>If you set <i>showRoller</i>, then dygraphs will combine the values as
 178       fractions. If two point are <i>a/b</i> and <i>c/d</i>, it will plot
 179       <i>(a+b) / (c+d)</i> rather than <i>(a/b + c/d) / 2</i>, which is what
 180       you'd get if you divided the fractions through. This will also shrink the
 181       confidence intervals.</li>
 182     </ul>
 183
 184     <h5>Standard Deviations</h5>
 185     <p>Often you have a measurement and also a measure of its uncertainty: a
 186     standard deviation. If you specify the <i>errorBars</i> option, dygraphs
 187     will look for alternating value and standard deviation columns in your CSV
 188     data.  Here's what it should look like:</p>
 189
 190     <code>
 191       new Dygraph(el,
 192                   "X,Y1,Y2\n" +
 193                   "1,10,5,20,5\n" +
 194                   "2,12,5,22,5\n",
 195                   { errorBars: true });
 196     </code>
 197
 198     <p>The "5" values are standard deviations. When each point is plotted, a
 199     2-standard deviation region around it is shaded, resulting in a 95%
 200     confidence interval. If you want more or less confidence, you can set the
 201     <i>sigma</i> option to something other than 2.0.</p>
 202
 203     <p>When you roll data with standard deviations, dygraphs will plot the
 204     average of your values in each rolling period and the RMS value of your
 205     standard deviations: sqrt(std1 + std2 + std3 + ... + stdN)/N.</p>
 206
 207     <h5>Custom error bars</h5>
 208     <p>Sometimes your data has asymetric uncertainty or you want to specify
 209     something else with the error bars around a point. One example of this is
 210     the "temperatures" demo on the <a href="http://danvk.org/dygraphs">dygraphs
 211       home page.</a>, where the point is the daily average and the bars denote
 212     the low and high temperatures for the day.</p>
 213
 214     <p>To specify this format, set the <i>customBars</i> option. Your CSV values
 215     should each be three numbers separated by semicolons ("low;mid;high").
 216     Here's an example:</p>
 217
 218     <code>
 219       new Dygraph(el,
 220                   "X,Y1,Y2\n" +
 221                   "1,10;20;30,20;5;25\n" +
 222                   "2,10;25;35,20;10;25\n",
 223                   { customBars: true });
 224     </code>
 225
 226     <p>The middle value need not lie between the low and high values. If you set
 227     a rolling period, the three values will all be averaged independently.</p>
 228
 229
 230     <a name="url"><h3>URL</h3>
 231     <p>If you pass in a URL, dygraphs will issue an XMLHttpRequest for it and
 232     attempt to parse the returned data as CSV.
 233     </p>
 234
 235     <p><i>Common problems</i>. Make sure the URL is accessible and returns data
 236     in text format (as opposed to a CSV file with an HTML header). You can see
 237     what the response looks like by checking your JS console or by requesting
 238     the URL yourself.</p>
 239
 240
 241     <a name="array"><h3>Array (native format)</h3>
 242     <p>If you'll be constructing your data set from a server-side program (or
 243     from JavaScript) then you're better off producing an array than CSV data.
 244     This saves the cost of parsing the CSV data and also avoids common parser
 245     errors.</p>
 246
 247     <p>The downside is that it's harder to look at your data (you'll need to use
 248     a JS debugger) and that the data format is a bit less clear for values with
 249     uncertainties.</p>
 250
 251     <p>Here's an example of "native format":</p>
 252
 253     <code>
 254       new Dygraph(document.getElementById("graphdiv2"),
 255                   [
 256                     [1,10,100],
 257                     [2,20,80],
 258                     [3,50,60],
 259                     [4,70,80]
 260                   ],
 261                   {
 262                     labels: [ "x", "A", "B" ]
 263                   });
 264     </code>
 265
 266     <h4>Headers</h4>
 267     <p>Headers for native format must be specified via the <i>labels</i>
 268     option. There's no other way to set them.</p>
 269
 270     <h4>x-values</h4>
 271     <p>If you want your x-values to be dates, you'll need to use specify a Date
 272     object in the first column. Otherwise, specify a number. Here's a sample
 273     array with dates on the x-axis:</p>
 274
 275     <code>
 276       [
 277         [ new Date("2009/07/12"), 100, 200 ],
 278         [ new Date("2009/07/19"), 150, 220 ]
 279       ]
 280     </code>
 281
 282     <h4>y-values</h4>
 283     <p>You can specify <i>errorBars</i>, <i>fractions</i> or <i>customBars</i>
 284     with the array format. If you specify any of these, the values become arrays
 285     (rather than numbers). Here's what the format looks like for each one:</p>
 286
 287     <code>
 288       <i>errorBars</i>: [x, [value1, std1], [value2, std2], ...]
 289       <i>fractions</i>: [x, [num1, den1], [num2, den2], ...]
 290       <i>customBars</i>: [x, [low1, val1, high1], [low2, val2, high2], ...]
 291     </code>
 292
 293     <p>To specify missing data, set the value to null. You may not set a value
 294     inside an array to null. Use null instead of the entire array.</p>
 295
 296     <a name="function"><h3>Functions</h3>
 297
 298     <p>You can specify a function that returns any of the other types. If
 299     <i>x</i> is a valid piece of dygraphs input, then so is</p>
 300
 301     <code>
 302       function() { return x; }
 303     </code>
 304
 305     <a name="datatable"><h3>DataTable</h3>
 306     <p>You can also specify a Google Visualization Library <a
 307       href="http://code.google.com/apis/visualization/documentation/reference.html#DataTable">DataTable</a>
 308     object as your input data. This lets you easily switch between dygraphs and
 309     other gviz visualizations such as the Annotated Timeline. It also lets you
 310     embed a Dygraph in a Google Spreadsheet.</p>
 311
 312     <p>You'll need to set your first column's type to one of "number", "date"
 313     or "datetime".</p>
 314
 315     <pre>
 316     DataTable TODO:
 317     - When to use Dygraph.GvizWrapper
 318     - how to specify fractions
 319     - how to specify missing data
 320     - how to specify value + std. dev.
 321     - how to specify [low, middle, high]
 322     - walkthrough of embedding a gadget in google docs/on a web page
 323     - walkthrough of using std. dev. in a spreadsheet chart
 324     </pre>
 325
 326   </body>
 327 </html>