How do you calculate the median for a variable in iReport? - jasper-reports

Question

I am preparing a report in iReport, and I need to calculate the median of a field for a variable that will be used in a crosstab. I noticed there is no built in calculation type for median (just highest and lowest).
Is there any way to get the median or 50th percentile of a field in iReport?

Answer 1

There is no builtin median calculation in JasperReports.
A median can still be obtained by manually collecting the values in a list and then using Apache Commons Math to do the computation.
See the following example. The report also uses Apache Commons Lang to convert a wrapper array to a primitive array. To run the report, you will need to add commons-math3-x.y.z.jar and commons-lang3-x.y.jar to the classpath.
<?xml version="1.0" encoding="UTF-8"?>
<jasperReport xmlns="http://jasperreports.sourceforge.net/jasperreports" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://jasperreports.sourceforge.net/jasperreports http://jasperreports.sourceforge.net/xsd/jasperreport.xsd" name="FirstJasper" columnCount="1" pageWidth="595" pageHeight="842" columnWidth="555" leftMargin="20" rightMargin="20" topMargin="30" bottomMargin="30">
<style name="Sans_Normal" isDefault="true" fontName="DejaVu Sans" fontSize="8"/>
<queryString>SELECT * FROM Orders</queryString>
<field name="Freight" class="java.lang.Double"/>
<variable name="FreightList" class="java.util.List">
<variableExpression>$V{FreightList}</variableExpression>
<initialValueExpression>new java.util.ArrayList()</initialValueExpression>
</variable>
<variable name="AddFreight" class="java.lang.Boolean">
<variableExpression>$V{FreightList}.add($F{Freight})</variableExpression>
</variable>
<title>
<band height="50">
<textField evaluationTime="Report">
<reportElement x="5" y="5" width="350" height="40"/>
<textFieldExpression><![CDATA["median is " + org.apache.commons.math3.stat.StatUtils.percentile(org.apache.commons.lang3.ArrayUtils.toPrimitive((Double[]) $V{FreightList}.toArray(new Double[$V{FreightList}.size()])), 50)]]></textFieldExpression>
</textField>
</band>
</title>
<detail>
<band height="13">
<textField pattern="0.00">
<reportElement x="5" y="0" width="350" height="11"/>
<textFieldExpression><![CDATA[$F{Freight}]]></textFieldExpression>
</textField>
</band>
</detail>
</jasperReport>