How to get points that do not intersect, R-CodePudding

I have two sets of points in coordinate system: A and B. All points in B are in A. So I want to pick the points in A which are not in B. I'm using the sf library, but I'm little stuck.

Here I show a reproducible exameple. Consider the next data.

fname <- system.file("shape/nc.shp", package="sf")
nc <- st_read(fname)
library(sp)
library(sf)
data(meuse)
coordinates(meuse) = ~x y

So I have the next two set of points A and B

A <- st_as_sf(meuse) %>% select(geometry) #155 obs
B <- filter(A, row_number()<= 100)%>% select(geometry) #100 obs

Starting from there, I want to rescue the points in A that are not in B, i.e., the remaining 55 points.

CodePudding user response：

Looks like you can use the %in% operator or the st_difference function. If using st_difference, you might need to st_combine each set individually if the points are sf but not if they're sfc.

The methods may differ a little depending on the type of data you're using. Are they just points(sfc), or are they points associated with data(sf)?

*Edit for your reproducible example:

library(dplyr)
library(ggplot2)
library(sp)
library(sf)

data(meuse)
coordinates(meuse) = ~x y

A <- st_as_sf(meuse) %>% select(geometry) #155 obs
B <- filter(A, row_number()<= 100)%>% select(geometry) #100 obs

diff_meuse <- st_difference(st_combine(A), st_combine(B)) %>% st_cast('POINT')

diff_meuse
#> Geometry set for 55 features 
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: 178786 ymin: 329714 xmax: 180923 ymax: 333116
#> CRS:           NA
#> First 5 geometries:
#> POINT (178786 329822)
#> POINT (178875 330311)
#> POINT (179024 329733)
#> POINT (179030 330082)
#> POINT (179034 330561)

ggplot()  
  geom_sf(data = A, size = 4, alpha = .3)   
  geom_sf(data = diff_meuse, color = 'red')

^{Created on 2022-03-31 by the}