How to add group band on combination of multiple fields?

Question

I have this data and I want in iReport is group this by number group and color group.

color | number_group | color_group |
red   |    1         |  primary    |
blue  |    1         |  primary    |
yellow|    2         |  primary    |
orange|    2         |  secondary  |
violet|    1         |  secondary  |
green |    1         |  secondary  |

I want in my report

Color Group: Primary   Number: 1
red
blue

Color Group: Primary   Number: 2
yellow

Color Group: Secondary Number: 1
violet
green

Color Group: Secondary Number: 2
orange

But in I can only manage to do Add Group > Group Criteria > Group by following expression > choose color_group field.

And the output is this which is not the one that I'm hoping for.

Color Group: Primary Number: 1
red
blue
yellow

Color Group: Secondary Number: 2
orange
violet
green

I think the right solution is using Add Group > Group Criteria > Group by following expression > group expression with text area but I don't know what to put there. Anyone?

Answer 1

Group on the concatenation of the two values:

<groupExpression><![CDATA[$F{number_group} + $F{color_group}]]></groupExpression>

Example

<?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="group" pageWidth="595" pageHeight="842" columnWidth="555" leftMargin="20" rightMargin="20" topMargin="20" bottomMargin="20" uuid="c1d9b4b7-6162-4b17-b871-3cf3b867d1ef">     
    <queryString>
        <![CDATA[]]>
    </queryString>
    <field name="color" class="java.lang.String"/>
    <field name="number_group" class="java.lang.String"/>
    <field name="color_group" class="java.lang.String"/>
    <group name="myGroup">
        <groupExpression><![CDATA[$F{number_group} + $F{color_group}]]></groupExpression>
        <groupHeader>
            <band height="20">
                <textField>
                    <reportElement mode="Transparent" x="0" y="0" width="300" height="20" forecolor="#3333FF" uuid="b3f3381f-26c1-48d5-953e-ddd017fbf7cf"/>
                    <textElement verticalAlignment="Middle"/>
                    <textFieldExpression><![CDATA["Color Group: " + $F{color_group} + " Number: " + $F{number_group}]]></textFieldExpression>
                </textField>
            </band>
        </groupHeader>
    </group>
    <detail>
        <band height="15" splitType="Stretch">
            <textField>
                <reportElement x="0" y="0" width="300" height="15" uuid="7337168a-363f-4438-a38e-e4859fb6fdd1"/>
                <textElement verticalAlignment="Middle"/>
                <textFieldExpression><![CDATA[$F{color}]]></textFieldExpression>
            </textField>
        </band>
    </detail>
</jasperReport>

Output

Note: The get exact same order as your expected output the orange record need to be last (order data)