Decoding Particular Element of JSON In PHP - php

Question

I am trying to decode JSON
I am reading the JSON through STOMP. There are different JSON datasets so I need to work out which JSON dataset has come through. I do this by reading its title.
However there is one particular dataset I am having trouble reading
foreach (json_decode($msg->body,true) as $event) {
if(isset($event['schemaLocation'])) {
$schedule_id=($event['schedule']['schedule_start_date']);
$signalling_id=($event['schedule']['schedule_segment']['signalling_id']);
echo $schedule_id;
}
In the above example the isset function works fine and also $schedule_id obtains the right answer
However the $signalling_id gives an error of Undefined index:
Here is a dump of PART of the JSON (Its rather long............).The piece of JSON with the signalling_id is towards the end of the JSON. Any help to get the variable signalling_id much appreciated.
array(7) {
["schemaLocation"]=>
string(72) "http://xml.networkrail.co.uk/ns/2008/Train itm_vstp_cif_messaging_v1.xsd"
["classification"]=>
string(8) "industry"
["timestamp"]=>
string(13) "1410374918000"
["owner"]=>
string(12) "Network Rail"
["originMsgId"]=>
string(47) "2014-09-10T18:48:38-00:00vstp.networkrail.co.uk"
["Sender"]=>
array(3) {
["organisation"]=>
string(12) "Network Rail"
["application"]=>
string(4) "TOPS"
["component"]=>
string(4) "VSTP"
}
["schedule"]=>
array(11) {
["schedule_id"]=>
string(0) ""
["transaction_type"]=>
string(6) "Create"
["schedule_start_date"]=>
string(10) "2014-09-10"
["schedule_end_date"]=>
string(10) "2014-09-10"
["schedule_days_runs"]=>
string(7) "0010000"
["applicable_timetable"]=>
string(1) "N"
["CIF_bank_holiday_running"]=>
string(1) " "
["CIF_train_uid"]=>
string(6) "W64017"
["train_status"]=>
string(1) "1"
["CIF_stp_indicator"]=>
string(1) "O"
["schedule_segment"]=>
array(1) {
[0]=>
array(20) {
["signalling_id"]=>
string(4) "5Y75"
["uic_code"]=>
string(0) ""
["atoc_code"]=>
string(0) ""
["CIF_train_category"]=>
string(2) "EE"
["CIF_headcode"]=>
string(0) ""
["CIF_course_indicator"]=
............................................

Answer 1

schedule_segment is itself an array, so instead of
['schedule']['schedule_segment']['signalling_id']);
that should probably be
['schedule']['schedule_segment'][0]['signalling_id']);

Answer 2

As you can see in the var dump, signalling_id is inside another array. Use:
$signalling_id=($event ['schedule']['schedule_segment'][0]['signalling_id']);
If that one element array with key 0 is not constant throughout, you may need some logic to figure out what it is in each iteration.