In arc2r/book: All things R Spatial or A guide to spatial R for Recovering ArcGIS Users

knitr::opts_chunk$set(echo = TRUE, warning = FALSE,message = FALSE)

library(sf)
library(dplyr)

set.seed(10)
nrows <- 10
circs <- data.frame(
  id = 1:nrows,
  x = rnorm(nrows),
  y = rnorm(nrows)
) %>%
  st_as_sf(coords = c(2,3)) %>%
  st_buffer(0.25)

circsplot <- ggplot(circs) + 
  geom_sf(fill = "blue",alpha = 0.3) +
  geom_sf_text(aes(label = id)) +
  theme_void()
circsplot

st_relate(circs,pattern = "2********")

crossmatrix <- st_relate(circs,pattern = "2********",sparse = FALSE)
crossmatrix[1:6,1:6] # only showing 6 since this prints nicely

# Remove the diagonals since it's simply each feature tested against itself
diag(crossmatrix) <- FALSE
error <- which(crossmatrix,arr.ind = TRUE) %>%
  as.vector() %>%
  unique()


circsplot +
  geom_sf(data = circs[error,], fill = "red", alpha = 0.3)

nc = st_read(system.file("shape/nc.shp", package="sf"), quiet = TRUE)

ggplot(nc) + 
  geom_sf() +
  theme_void()

nc_union <- st_union(nc)
nc_union

nc_singlepart <- nc_union %>%
  st_cast("POLYGON")%>%
  st_sf() %>%
  mutate(id = 1:n())

ggplot(nc_singlepart) +
  geom_sf(aes(fill = factor(id))) +
  labs(fill = "id") +
  theme_void()

map_lgl(nc_singlepart$geometry,~length(.x)== 1)

holes <- nc_singlepart %>%
  st_union() %>%
  st_centroid() %>%
  st_buffer(0.5)

nc_holes <- st_difference(nc_singlepart,holes)

ggplot(nc_holes) + 
  geom_sf() +
  theme_void()

map_lgl(nc_holes$geometry,~length(.x)== 1)

arc2r/book documentation built on March 5, 2021, 2:10 p.m.