There are a number of ways of filtering your data. What kind of filter are you hoping to achieve? Are you trying to filter out certain frequencies?
At its simplest, you could use an Express VI to downsample your signal. The Sample Compression Express VI in the Signal Manipulation express palette gives you the options to reduce your samples by a certain factor. It also lets you choose which algorithm to use for the compression (averaging, median, etc.). I've attached an example that uses it. You could also average your data using shift registers, but the Express VIs the absolute easiest solution.
I've attached an example from LabVIEW 7.1 to show this.
Jarrod S.
National Instruments
