Unable to get array elements from log field using NRQL - getfield

I am logging some user values like FPS, Latency in the form of an array.

Log format is like:
log_data.report.fps : [15, 30, 20, 30, 29, 6, 11, 10, 9, 10]

This information is reported every 10 seconds - one record in the array for each second.

All I want to do is - get the nth element from the array.

I tried - getfield(log_data.report.fps,2) but, it returns null every time.

I think the problem is that new relic is considering the array as a string instead of an array.

How do I fix it?

Please help.