# erode.hexbin

##### Erosion of a Hexagon Count Image

This erosion algorithm removes counts from hexagon cells at a rate proportional to the cells' exposed surface area. When a cell becomes empty, algorithm removes the emptied cell and notes the removal order. Cell removal increases the exposure of any neighboring cells. The last cell removed is a type of bivariate median.

- Keywords
- hplot

##### Usage

```
erode(hbin, cdfcut = 0.5)
erode.hexbin(hbin, cdfcut = 0.5)
```

##### Arguments

- hbin
an object of class

`hexbin`

.- cdfcut
number in (0,1) indicating the confidence level for the limits.

##### Details

The algorithm extracts high count cells with containing a given fraction (cdfcut) of the total counts. The algorithm extracts all cells if cdfcut=0. The algorithm performs gray-level erosion on the extracted cells. Each erosion cycle removes counts from cells. The counts removed for each cell are a multiple of the cell's exposed-face count. The algorithm choses the multiple so at least one cell will be empty or have a count deficit on each erosion cycle. The erode vector contain an erosion number for each cell. The value of erode is

6*erosion\_cycle\_ at\_ cell\_ removal - cell\_deficit\_at\_removal

Cells with low values are eroded first. The cell with the highest erosion number is a candidate bivariate median. A few ties in erode are common.

##### Value

An `"erodebin"`

object (with all the slots from `hbin`

) and
additionally with
high count cells and a component `erode`

that gives the erosion order.

##### See Also

`hexbin`

, `smooth.hexbin`

,
`hcell2xy`

,
`gplot.hexbin`

,
`grid.hexagons`

, `grid.hexlegend`

##### Examples

`library(hexbin)`

```
# NOT RUN {
set.seed(153)
x <- rnorm(10000)
y <- rnorm(10000)
bin <- hexbin(x,y)
smbin <- smooth.hexbin(bin)
erodebin <- erode.hexbin(smbin, cdfcut=.5)
plot(erodebin)
## bivariate boxplot
hboxplot(erodebin, main = "hboxplot(erodebin)")
# }
# NOT RUN {
<!-- %% MM: This looks wrong -- both the graphic and the logic in "par" here : -->
# }
# NOT RUN {
# show erosion order
plot(bin,style= "lat", minarea=1, maxarea=1,
legend=FALSE, border=gray(.7))
# }
# NOT RUN {
<!-- %% FIXME: {compare with example in "hexbin0"} -->
# }
# NOT RUN {
grid.hexagons(erodebin,style= "lat", minarea=1, maxarea=1,pen="green")
xy <- hcell2xy(erodebin)
library("grid")
grid.text(lab = as.character(erodebin@erode), xy$x, xy$y,
gp = gpar(col="white", cex=0.65))
# }
```

*Documentation reproduced from package hexbin, version 1.27.1, License: GPL-2*