Average & Standard Deviation Loop

Hello to anyone who can help:

I am working on a research project and I was looking for some hlep in writing a program. What I want the program to do is to take the average and standard deviation of a varying set of values and then reject any values which fall beyond 1 standard deviation from the average. Ideally the program would retake the average and standard deviation and reject any values which fall beyond 1 standard deviation from this new average. I would like this to loop until the standard deviation is less than a certain number (ie: 0.5). I know excel already has functions to take averages and standard deviations but if someone knows of a program like this that exists or could give me some advice on how to go about this, it would be greatly appreciated.

Best,
Sean