My new favorite Graphite function – percentileOfSeries:
percentileOfSeries returns a single series which is composed of the n-percentile values taken across a wildcard series at each point. Unless interpolate is set to True, percentile values are actual values contained in one of the supplied series.
I came across percentileOfSeries while looking for a way to combine several data points into a single trend. It does a good job of solving that problem.