Selecting the min/max value of an attribute under multiple nodes in XPath 1.0

Question

Consider the following XML structure:

<a>
<b>
    <c>
        <d x="1"/>
        <d x="2"/>
        <d x="3"/>
        <d x="3"/>
        <d x="4"/>
    </c>
</b>
<b>
    <c>
        <d x="1"/>
        <d x="1"/>
        <d x="2"/>
        <d x="3"/>
        <d x="4"/>
        <d x="5"/>
        <d x="5"/>
    </c>
</b>
<b>
    <c>
        <d x="1"/>
        <d x="2"/>
        <d x="3"/>
        <d x="3"/>
        <d x="4"/>
        <d x="5"/>
        <d x="5"/>
    </c>
</b>

I'd like a XPath 1.0 statement to give me the minimum and maximum values of @x? So far I have the following for the minimum:

//a/b/c/d[not(preceding-sibling::d/@x <= @x) and not(following-sibling::d/@x <= @x)]/@x

which is close, but no cigar :-(

Any help greatly appreciated!

Thanks, J

Answer 1

To fetch the maximum value, look for all attribute values for which there are not smaller ones. If there are multiple results, take the first one - they must be equal.

(//@x[not(. < //@x)])[1]

For the minimum value, just replace < by >.

For completeness reasons: if your XPath engine supports XPath 2.0 (or better), just use max(//@x) respecting min(//@x) which will probably be faster and more readable.