LabVIEW
Enqueue element only if it is an updated value
Store the previous incoming data in a shift register. Compare the previous data to the new incoming data. Stick your "Enqueue Element" inside the "True" case of a case structure. Update the shift register with the most recent data.
Here's a picture (incomplete, obviously, as there's no timing in the loop, nor does it have a stop button, plus the queue has no input queue reference, but I expect you can handle those parts nicely on your own):
That's the simplest way I can think of.
At todays copper prices, a solution with less wires is preferable. 😄
I typically use a globally initialized feedback node. Make sure to initialize it with something that normally does not occur in your data (NaN, Inf, empty string, -1, etc.)
