<select id="dropdown">
<?php
    // this PHP is essentially the same as in the above example
    $users = [
		[
			"forename"=>"a_name",
			"dob"=>"never",
			"height"=>"too_tall",
			"weight"=>"too_heavy",
			"nationality"=>"martian"
		],
		[
			"forename"=>"second_name",
			"dob"=>"always",
			"height"=>"too_short",
			"weight"=>"too_light",
			"nationality"=>"moon"
		],
		[
			"forename"=>"third_name",
			"dob"=>"forever",
			"height"=>"300ft",
			"weight"=>"2000lb",
			"nationality"=>"Earth"
		]
	];
    $userDataArray = []; // multidimensional array
    $user_id = 0;
    foreach($users as $user) {
        $data = $user["forename"];
        echo "<option value='$user_id'>$data</option>";
        $user_id++;
        $userDataArray[] = [ "forename"=>$user["forename"], "dob"=>$user["dob"], "height"=>$user["height"], "weight"=>$user["weight"], "nationality"=>$user["nationality"] ];
        // index 0 = forename, 1 = DOB, 2 = height, 3 = weight, 4 = nationality
    }
?>
</select><br />
<span id="display"></span>
<script src="https://a...content-available-to-author-only...s.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script><!-- load jQuery library -->
<script>
    var users = [
        <?php  // translate PHP array to JS one
            foreach($userDataArray as $user) {
                echo "{ forename: '" . $user["forename"] . "', dob: '" . $user["dob"] . "', weight: '" . $user["weight"] . "', height: '" . $user["height"] . "', nationality: '" . $user["nationality"] . "'},";
            }
        ?>
    ];
    $("#dropdown").change(function() {
		var i = $("#dropdown").val();
        $("#display").html("Name: " + users[i].forename + "<br />DOB: " + users[i].dob + "<br />Weight: " + users[i].weight + "<br />Height: " + users[i].height + "<br />Nationality: " + users[i].nationality);
    });
</script>

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