svn-gvsig-desktop / trunk / org.gvsig.desktop / org.gvsig.desktop.library / org.gvsig.expressionevaluator / org.gvsig.expressionevaluator.swing / org.gvsig.expressionevaluator.swing.impl / src / main / resources / org / gvsig / expressionevaluator / swing / jexpressionbuilder / en / description.html @ 44602
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<html>
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<body>
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<h2 id="expression-builder">Expression Builder</h1> |
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<p>This is the interface to generate expressions. An expression is an operation between values and it can be use for multiple porpouse: filters, operations, generate labels, etc.</p> |
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<p>An expression can contain:</p> |
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<ul>
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<li>Constants: a number <em>15</em>, or string <em>'id'</em>, etc.</li> |
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<li>Variables: like the name of a field <em>"Field1"</em> in vectorial layers. If the field just contain letters, numbers or _, it's not necessary the use of quotes.</li> |
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<li>Functions: like the <em>RAND()</em> function to generate a random number</li> |
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</ul>
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<p>In some cases you will be able to see a preview of the result of one execution of the expression under the text box.</p> |
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<p>You can search for operators or functions in the left panel. Once one category is selected, you'll be able to search in the middle panel by name of the function. For example: <em>RA</em>. The search will return functions like <em>RADIANS</em>, <em>RAND</em>... This search will be the same as use: <em>RA*</em>.</p> |
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<p>For fields in the layer, you will see in the middle panel a preview of all the values that contains each field so you will be able to select a specific value.</p> |
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<p>All the expressions used will be save in the History. You will find this button in the top right of the panel. The history just contain the last 20 used expressions. If you want to save an specific expression use the button next to the history button to add a Bookmark.</p> |
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</body>
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</html>
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