php ทำไฟล์ json โดยการวน loop ตามตัวอย่างแบบนี้ ต้องเขียนอย่างไรครับ

<?php

$s = <<<'EEE'
{
  "type": "FeatureCollection",
  "features":
    [
        {
            "type": "Feature",
            "properties": {
              "letter": "G",
              "color": "blue"
            },
            "geometry": {
              "type": "Polygon",
              "coordinates": [
                [
                  [123.61, -22.14], [122.38, -21.73],  [123.61, -22.14]
                ]
              ]
            }
        }
    ]
}
EEE;


echo '<pre>';
echo var_export(json_decode($s,true),1);
echo json_last_error_msg();

$x = array('123.61','122.38','123.61');
$y = array('-22.14','-21.73','-22.14');
$data=array();
$numRow = count($x);

for($i=0;$i<$numRow;$i++){
		$resules=array(
			$x[$i],
			$y[$i]
			);
	array_push($data, $resules);
}


echo json_encode($data);

$a = (object)array(
	"type"=>"FeatureCollection",
	"features"=>array(
		(object)array(
			"type"=>"Feature",
			"properties"=>(object)array(
				"letter"=>"G",
				"color"=>"blue",
			),
			"geometry"=>(object)array(
				"type"=>"Polygon",
				"coordinates"=>array(
					array(
						array(123.61, -22.14), array(122.38, -21.73),  array(123.61, -22.14)
					)
				)
			)
		)
	)
);