A list including the return value for the first call to hist (itself a list)
and the values for the bar heights.
Arguments
x
a list of numeric vectors
beside
plot histogram bars for groups side-by-side?
freq
logical; if 'TRUE', the histogram graphic is a representation
of frequencies, the 'counts' component of the result; if
'FALSE', probability densities, component 'density', are
plotted (so that the histogram has a total area of one).
Defaults to 'TRUE' if 'probability' is not specified
(does not consider equidistant breaks as in hist)