CODEWITHSUNDEEP
rggplot2
statslearner
statslearner

Reputation: 31

Extract area of polygons from ggvoronoi

I'd like to extract the areas each observation from ggvoronoi such that I get a new dataframe with the first column being the observation and the next column being the area of the polygon. 

library(ggvoronoi)
set.seed(45056)
x <- sample(1:200,100)
y <- sample(1:200,100)

ggplot(points,aes(x,y)) +
stat_voronoi(geom=“path”) +
geom_point()

Upvotes: 3

Views: 313

Answers (2)

kib
kib

Reputation: 61

ggvoronoi uses the deldir library to compute Voronoi tessellation. deldir returns a list of objects, which has a summary data frame for the points triangulated and the areas you are looking for.

You could run deldir on the same input to get the areas - dir.area column in the summary. For example:

?deldir

x = c(0, 1)
y = c(0, 1

d = deldir(x, y)

> d$summary
  x y n.tri del.area del.wts n.tside nbpt dir.area dir.wts
1 0 0     0        0     NaN       1    2     0.72     0.5
2 1 1     0        0     NaN       1    2     0.72     0.5

Upvotes: 0

mharinga
mharinga

Reputation: 1780

First convert your data to a sf object: 

library(sf) 
set.seed(45056)
x <- sample(1:200,100)
y <- sample(1:200,100)
points <- data.frame(x = x, y = y)   
points_sf <- st_as_sf(points, coords = c("x", "y"))

Then you can use the following functions to calculate the area of each polygon:

v <- points_sf %>% 
  st_union() %>%
  st_voronoi() %>%
  st_collection_extract() %>%
  st_area()

Combine with the original data:

cbind(x, y, v)

Upvotes: 1

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