Looping through JSON response + in JMETER

Question

I am using Jmeter for performance testing and stuck at following point: I am getting a JSON response from Webapi as follows:

PersonInfoList:
Person
[0]
{
  id: 1
  name: Steve
}
[1]
Person
{
  id: 2
  name: Mark
}

I need to get the ids based on the count of this JSON array and create a comma separated string as ("Expected value" = 1,2)

I know how to read a particular element using JSON Post processor or Regex processor but am unable to loop through the array and create a string as explained so that I can use this value in my next sampler request.

Please help me out with this: I am using Jmeter 3.0 and if this could be achieved without using external third party libs that would be great. Sorry for the JSON syntax above