Is there an easy way to apply a low-pass or high-pass filter to an array in MATLAB? I'm a bit overwhelmed by MATLAB's power (or the complexity of mathematics?) and need an easy function or some guidance as I couldn't figure it out from the documentation or searching the web. 

Answers:

Look at the filter function. 

If you just need a 1-pole low-pass filter, it's 

xfilt = filter(a, [1 a-1], x);

where a = T/τ, T = the time between samples, and τ (tau) is the filter time constant. 

Here's the corresponding high-pass filter: 

xfilt = filter([1-a a-1],[1 a-1], x);

If you need to design a filter, and have a license for the Signal Processing Toolbox, there's a bunch of functions, look at fvtool and fdatool.