Calculates the correlation coefficient between xs and ys as
sum[(xi-<x>)*(yi-<y>)]
r=----------------------
sx*sy
where <x>, <y> are the mean of dataset xs and ys, and, sx and sy are the
standard deviations.
Decorator to wrap functions that take a list of float values. In addition to
passing in a list of float values directly, it is possible to extract the
values from attributes or generic properties.