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<h2>
6. Iterators and filters</h2>
<blockquote>
<p>
<b> <a href="iterators.html#Introduction">6.1 Introduction</a> </b>
</p>
<p>
<b><a href="iterators.html#Component">6.2 Data table iterator</a></b>
</p>
<p>
<b><a href="iterators.html#Series">6.3 Data table series</a></b>
</p>
<p>
<b><a href="iterators.html#Filtration">6.4 Filtration</a></b>
</p>
</blockquote>
<h2>
<a name="Introduction">6.1 Introduction </a></h2>
<blockquote>
<p>
Some operations are required to be iterated. Typical example of iteration is reading
of
rows from data table. Iterators
are used for creation of selections for research.
Another example is creation of star's models array from database. Typically
an iterator requres a filtration that omit some steps of iteration process. In
priciple filtration may be performed with use of SQL. However SQL is a very poor language and
does not enable performing all kinds of filtration. The formula editor is used
for filtration in this software.</p>
<p>
</p>
</blockquote>
<h2>
<a name="Component">6.2 Data table iterator</a></h2>
<p>
Database iterator is a client of <a href="database.html#Component">query component</a> component corresponds to the
<img alt="Database comoponent" src="images/datasetiteratorbutton.jpg" />
button. It performs iterative reading of rows of SQL query. As a client of query component
it shold be connected to <a href="database.html#Component">query component</a> .
It is shown on the following picture:</p>
<p>
<img alt="Iterator + query" src="images/queryplusiterator.jpg" /> </p>
<p>
It is possible to process result of iteration. For example a user can link an
<a href="infoproccessing.html#Functionaltransformer"> functional transformer </a> to an iterator like it is exhibited on the following picture:</p>
<p>
<img alt="Combination" src="images/queryplusiteratorplusformula.jpg" /> </p>
<p>
</p>
<h2>
<a name="Series">6.3 Data table series</a></h2>
<p>
Let us consider an example of application of this iterator.
User should install <a href="hipandtycho.html">
TYCHO and HIPPARCOS DATABASE</a> to reproduce this example. Configuration of
this example is exhibited on the following picture:</p>
<p>
<img alt="Data series scenario" src="images/iteratorseriesscn.jpg" /> </p>
<p>
We have a catalogue of stars and wish to construct Herzsprung-Rassel diagram. The
catalogue contains parallaxes and magnitudes of stars. Herzsprung-Rassel diagram
requires absolute magnitudes of stars. Formula editor provides the calculation of
absolute star magnitude. The component <strong>Graph</strong> shows the following
diagram</p>
<p>
<img alt="Diagram" src="images/iteratorseries.jpg" /> </p>
<p>
<a href="cfa/dataseries.cfa">Click here to download this situation</a>.</p>
<h2>
<a name="Filtration"> 6.4 Filtration</a></h2>
Filtration of iterator output may be performed by the filter <img alt="Filter" src="images/filterbtn.JPG" />
. Let us consider an example of a filter application. The problem depends on construction
of Herzsprung-Rassel diagram with filtration of bad data. Data is bad if three
times of root-mean-square error of a parallax exceeds a parallax. The situation with filter is exhibited on the following picture:<br />
<br />
<br />
<p>
<img alt="Filtration" src="images/filteredseriesscn.jpg" />
</p>
<p>
A filter contains a formula that returns a Boolean output. Its editor of properties
looks like:</p>
<p>
<img alt="Filter properties" src="images/filterprop.jpg"/> </p>
<p>
The result diagram looks like:</p>
<p>
<img alt="Filtered diagram" src="images/filteredseries.jpg" /> </p>
<p>
User should install <a href="hipandtycho.html">
TYCHO and HIPPARCOS DATABASE</a> to reproduce this example. <a href="cfa/filterscn.cfa">
Click here to download this situation</a> .</p>
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Ph. D. Petr Ivankov worked as scientific researcher at Russian Mission Control Centre since 1978 up to 2000. Now he is engaged by Aviation training simulators http://dinamika-avia.com/ . His additional interests are:
1) Noncommutative geometry
http://front.math.ucdavis.edu/author/P.Ivankov
2) Literary work (Russian only)
http://zhurnal.lib.ru/editors/3/3d_m/
3) Scientific articles
http://arxiv.org/find/all/1/au:+Ivankov_Petr/0/1/0/all/0/1
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