Hexagon Bin Smoothing
"hexbin" (hexagon bin) object, compute a discrete
kernel smoother that covers seven cells, namely a center cell and its
six neighbors. With two iterations the kernel effectively covers
object of class
numeric vector of length 3 for relative weights of the center, the six neighbor cells, and twelve second neighbors.
This discrete kernel smoother uses the center cell, immediate neighbors and second neighbors to smooth the counts. The counts for each resulting cell is a linear combination of previous cell counts and weights. The weights are
|1 center cell,||weight = wts|
|6 immediate neighbors||weight = wts|
|12 second neighbors||weight =wts|
If a cell, its immediate and second neighbors all have a value of
max(cnt), the new maximum count would be
max(cnt)*sum(wts). It is possible for the counts to overflow.
The domain for cells with positive counts increases. The hexbin
reflect this increase.
Note that usually
dimen = xbins+1.
The intent was to provide a fast, iterated, immediate neighbor smoother. However, the current hexbin plotting routines only support shifting even numbered rows to the right. Future work can
(1) add a shift indicator to hexbin objects that indicates left or
(2) generalize plot.hexbin() and hexagons()
(3) provide an iterated kernel.
wts=0, the smoother only uses the immediate neighbors.
With a shift indicator the domain could increase by 2 rows (one bottom
and on top) and 2 columns (one left and one right). However the current
implementation increases the domain by 4 rows and 4 columns, thus
reducing plotting resolution.
an object of class
"smoothbin", extending class
The object includes the additional slot
1 2 3 4 5 6 7 8 9 10 11 12 13
x <- rnorm(10000) y <- rnorm(10000) bin <- hexbin(x,y) # show the smooth counts in gray level smbin <- smooth.hexbin(bin) plot(smbin, main = "smooth.hexbin(.)") # Compare the smooth and the origin smbin1 <- smbin smbin1@count <- as.integer(ceiling(smbin@count/sum(smbin@wts))) plot(smbin1) smbin2 <- smooth.hexbin(bin,wts=c(1,0,0)) # expand the domain for comparability plot(smbin2)