How can I use xsl 1.0 for sort by group and output to xml again?

[jatuphum]

Hi all,

I have xml like these below.

<Listing>
    <Avail>
        <Field1>aaa</Field1>
        <Field2>800</Field2>
        <Field3>900</Field3>
        <SortValue>20.00</SortValue>
    </Avail>
    <Avail>
        <Field1>aaa</Field1>
        <Field2>800</Field2>
        <Field3>900</Field3>
        <SortValue>10.00</SortValue>
    </Avail>
    <Avail>
        <Field1>bbb</Field1>
        <Field2>1300</Field2>
        <Field3>1500</Field3>
        <SortValue>35.05</SortValue>
    </Avail>
    <Avail>
        <Field1>bbb</Field1>
        <Field2>1300</Field2>
        <Field3>1500</Field3>
        <SortValue>20.80</SortValue>
    </Avail>
    <Avail>
        <Field1>ccc</Field1>
        <Field2>1500</Field2>
        <Field3>1900</Field3>
        <SortValue>40.00</SortValue>
    </Avail>
</Listing>

Then I want to ascending sort "SortValue" within group by "Field1", "Field2" and "Field3" above XML to
new XML output like this below.

<Listing>
    <Avail>
        <Field1>aaa</Field1>
        <Field2>800</Field2>
        <Field3>900</Field3>
        <SortValue>10.00</SortValue>
    </Avail>
    <Avail>
        <Field1>aaa</Field1>
        <Field2>800</Field2>
        <Field3>900</Field3>
        <SortValue>20.00</SortValue>
    </Avail>
    <Avail>
        <Field1>bbb</Field1>
        <Field2>1300</Field2>
        <Field3>1500</Field3>
        <SortValue>20.80</SortValue>
    </Avail>
    <Avail>
        <Field1>bbb</Field1>
        <Field2>1300</Field2>
        <Field3>1500</Field3>
        <SortValue>35.05</SortValue>
    </Avail>
    <Avail>
        <Field1>ccc</Field1>
        <Field2>1500</Field2>
        <Field3>1900</Field3>
        <SortValue>40.00</SortValue>
    </Avail>
</Listing>

I try to sort my using "SortValue" field but I don't know,
How can I use XSL 1.0 for sort by group?

Thank you very much.