Summarizes data using a sliding window without loops

This function will summarize a 1-D vector of data (i.e. 1 column) based on what the user specifies as the statistic (e.g. mean, sum, etc.). It uses no loops, so it is extremely fast. However, it will use up memory as a result. I've included memory checks such that if you do not have enough memory, it will perform the moving summary using loops. Thus what would take a few seconds, will take minute(s).

The function will summarize data over a moving window incrementing one value at a time. For example, if data are hourly and the user wants a 7-day average (i.e. 168 hours), the average will be computed for each 1-hour increment, sliding the 7-day window 1-hour at a time.

UPDATED: 10/14/2010 - streamlined function, uses less memory.
UPDATED: 10/14/2010 - no more guessing on memory usage. Exact solution is used.

Example syntax:
dataout = movingstat(datain,20,@sum);