Finding the first entry of XML and displaying it

Im working on compiling a list using XML and PHP. I’m looking to find the first “destination tag” found in the RailVehicleStateClass for each train ID and echo it out. I tried doing a foreach loop to gather the destination tag but it just loops the same data for each train ID until the end of the xml file. Below is a snippet of the XML file, the full version has well over 700 entries and each train can have anywhere from 1 to 100+ railvehiclaes associated with it.

XML

<ScnLoader xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <trainList>
        <TrainLoader>
            <trainID>99991</trainID>
            <TrainWasAI>false</TrainWasAI>
            <DispatchTrainDirection>0</DispatchTrainDirection>
            <ManuallyAppliedSpeedLimitMPH>2147483647</ManuallyAppliedSpeedLimitMPH>
            <PreviousSignalInstruction>Clear</PreviousSignalInstruction>
                <unitLoaderList>
                    <RailVehicleStateClass>
                        <destinationTag>TRC SVMS</destinationTag>
                    </RailVehicleStateClass>
                    <RailVehicleStateClass>
                        <destinationTag>PRC</destinationTag>
                    </RailVehicleStateClass>
            </unitLoaderList>
        </TrainLoader>
    </trainList>
</ScnLoader>

PHP

 <?php
            $trains = simplexml_load_file("Auto%20Save%20World.xml") or die("Error: Cannot create object");   
            $totalUnitCount=0;
            echo "<table>";
                echo "<th>#</th>";
                echo "<th>Train ID</th>";
                echo "<th>Symbol</th>";
                echo "<th>Direction</th>";
                echo "<th>AI</th>";
            foreach ($trains->xpath("//TrainLoader") as $train) {
                $totalUnitCount = $totalUnitCount + 1;

                foreach (array_slice($trains->xpath("//RailVehicleStateClass"),0,1) as $unit){
                    echo $unit->destinationTag;
                }
                echo "</td>";
                echo "<td>";
                echo $train->DispatchTrainDirection;
                echo "</td>";
                echo "<td>";
                echo $train->TrainWasAI;
                echo "</td>";
            }

            ?>

Answer

Your xpath query to get the RailVehicleStateClass elements needs to be made relative to the current $train. You can do that using:

$train->xpath(".//RailVehicleStateClass")

Note the use of . in front of // to make the path relative to the current $train element.