Create data buffer with arrays

Question

Hello.. I'm trying to create a data buffer but I can't...(I don't understand very well how to use the shift registers, feedback, auto-index, etc.) I receive real-data from 16 sources and I want the buffer to allocate 20 samples or so... (20 x 16 matrix or array). I'm trying to simulate the sources and using replace array subset, but I can't do what I want.. (that a single data fill the space in index 0, and when a value reaches index 19, the next number replace the one in index 0 and so on....)
I want to create a buffer for when some disturbance ocurrs, I want to save the data from 1 or 2 seconds before the event. I think that I can use too a history data property node, but I'm not using a waveform chart anymore, because I want also the time stamp of the data in the xscale.. and with the chart I didn't manage to do it... (I tried with an offset property node.. but eventually the time in the xscale lagged the real time, I think that happens because the rate sample is not constant... but that's another problem.. =S)
Thanks in advance for all your help...   Mitzi
PS. I attach my attempt...
Attachments:
buffer_qst.vi ‏20 KB

Answer 1

If you want a build a 20x16 array with only the 20 most recent values, what you can do is use the build array function to concatenate on the end of the data (you will need a shift register for this). 
Next take the output of the build array and get the last 20 columns using the array subset function.
(There's a real clever way to do this involving reversing the arrays, but I'm not going to confuse you with that).
If you're still not getting it when I get home, I'll write up a VI and post it.  What version are you using?
-Matt Bradley
************ kudos always appreciated, but only when deserved **************************