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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Different types of NULL data handling</title><link rel="stylesheet" type="text/css" href="manual.css"><meta name="generator" content="DocBook XSL Stylesheets V1.76.0"><link rel="home" href="index.html" title="JpGraph Manual"><link rel="up" href="ch13.html" title="Chapter 13. Getting hold of the data to be displayed"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Different types of NULL data handling</th></tr><tr><td width="20%" align="left"> </td><th width="60%" align="center">Chapter 13. Getting hold of the data to be displayed</th><td width="20%" align="right"> </td></tr></table><hr></div><div class="sect1" title="Different types of NULL data handling"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sec1.null-value-handling"></a>Different types of NULL data handling</h2></div></div></div>
<p>In some data there might be data points missing. For example if some experimental
data is to be graphed there can be data points where the equipment was faulty and
not valid values exist. The library offers to way to handle this. </p>
<p>
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<p>Leave the data point empty and leave a whole in the graph, for example
a break in a line plot. This happens iof the null value is specified as
either one of the following values</p>
<p>
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
<p><code class="code">'x'</code> - A single character 'x'</p>
</li><li class="listitem">
<p><code class="code">''</code> - An empty string</p>
</li><li class="listitem">
<p><code class="code">NULL</code> - The NULL value</p>
</li></ul></div><p>
</p>
</li><li class="listitem">
<p>Ignore the data point and connect the previous and next data point
with the line in a line graph. This is accomplished by specifying the
null value as</p>
<p>
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">
<p><code class="code">'-'</code> - A single hyphen character</p>
</li></ul></div><p>
</p>
</li></ol></div><p>
</p>
<p>In <a class="xref" href="ch13s06.html#ex.different-nulls" title="Example 13.1. Illustration of different types of NULL values in graphs">Example 13.1. Illustration of different types of NULL values in graphs</a> an example with the different types of
null values are shown. In these graphs the third data point is set to null with the
two different null values.</p>
<p>
</p><div class="example"><a name="ex.different-nulls"></a><p class="title"><b>Example 13.1. Illustration of different types of NULL values in graphs</b></p><div class="example-contents">
<div class="informaltable">
<table border="0"><colgroup><col class="c1"><col class="c2"><col class="c3"></colgroup><tbody><tr><td>
<div class="figure"><a name="id2539277"></a><p class="title"><b>Figure 13.4. Original graph with all values</b></p><div class="figure-contents">
<div class="mediaobject"><img src="images/nullvalues1.png" alt="Original graph with all values"></div>
</div></div><br class="figure-break">
</td><td>
<div class="figure"><a name="id2539306"></a><p class="title"><b>Figure 13.5. Value at x=2 as ''</b></p><div class="figure-contents">
<div class="mediaobject"><img src="images/nullvalues2.png" alt="Value at x=2 as ''"></div>
</div></div><br class="figure-break">
</td><td>
<div class="figure"><a name="id2539330"></a><p class="title"><b>Figure 13.6. Value at x=2 as '-'</b></p><div class="figure-contents">
<div class="mediaobject"><img src="images/nullvalues3.png" alt="Value at x=2 as '-'"></div>
</div></div><br class="figure-break">
</td></tr></tbody></table>
</div>
</div></div><p><br class="example-break">
</p>
<p>
</p><div class="caution" title="Caution" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Caution</h3>
<p>If all values in a line plot are null values an error will be shown since
this is not considered to be a valid plot.</p>
<p>
</p><div class="figure"><a name="fig.only-null-error"></a><p class="title"><b>Figure 13.7. Error when only null values are specified</b></p><div class="figure-contents">
<div class="mediaobject"><img src="images/errmsg-only-null.png" alt="Error when only null values are specified"></div>
</div></div><p><br class="figure-break">
</p>
</div><p>
</p>
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