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