Compute a histogram from xy data given set of breakpoints.
data.frame, or object coercible to a
as.data.frame(), where the columns of the
or can be, interpreted as XY coordinates.
List. A list of vectors, one for each dimension of
each vector gives the breakpoints between the histogram cells.
A list with three components:
x The X dimension breakpoints.
y The Y dimension breakpoints.
z A frequency table of the number of
xy points in each cell.