How do you generate random data info using json and spry?

Question

I have a mobile applicaton that uses spry datasets that dynamically populate a jquery mobile listview by using a json file. Everything is operating as it should.
However, I would like to understand how to pull random objects from the json file to have them displayed on a different page.
My json file is standard and not complicated. It has several levels. Each is represented as below:
                              { "Level1":
                                                            {"imageurl":"images/_myimage.png",
                                                            "someData":"S,A,P,R",
                                                            "levelLongDesc":"further description",
                                                            "name": "John Doe",
                                                            "page": "referencepage",
                                                            "description":"The description of the image"
{"imageurl":"images/_myimage.png",
  "someData":"S,A,P,R",
  "levelLongDesc":"further description",
  "name": "John Doe",
  "page": "referencepage",
  "description":"The description of the image"
Json file Level1 has about 70 objects
What I would like to do is randomly load one of the Level1 object arrays into the page when the user selects a Level 1 radio button that is on the screen. I know how to create the page, radio buttons and basics, but just don't know how to pull in the random data.
I've found one code sample on this site that speaks to spry and xml, but I haven't been able to apply it in any way that works for me with the json file:
http://forums.adobe.com/message/662551
I've also googled. There isn't much on spry datasets with json and generating random info. There was a little bit on sorting, but that didn't help either.
Does anyone have a good example/tutorial of how to use the random function with spry/json?
TIA
-Rachel

Answer 1

I've done similar things before.  A few thoughts for you:
1. I'm assuming you're doing a buffered period or frequency measurement on the incoming encoder pulses, right?  First key point is that you'll have data that is spaced equally in position, but not equally in time.  If you are looking for a time-based FFT such that increasing speed will shift your spectrum, you're going to need to go through an interpolation process to resample your data as though equally-spaced in in time. 
2. Your 149 pulse per rev encoder may be a significant source of error unless its 149 pulses are placed with extreme accuracy.  Any error in pulse placement violates your underlying assumption of data that is equally-spaced in position.  It'll be very helpful to send your data through a software lowpass filter to attenuate those artifacts. 
3. I am not sure what you mean by "decompose the buffered data (array) into a single datastream."  You'll get an array of periods / frequencies from the call to DAQmx Read.  If you want to use it in a LabVIEW waveform datatype, you'll first need to do the resampling to create equally-spaced-in-time data.  The LabVIEW waveform datatype (and all the analysis functions like FFT that use it) depend on receiving data with a fixed constant time interval between samples.
-Kevin P.