Using two grouping designations to create one 'combined' grouping variable

Question

Given a data.frame:

df <- data.frame(grp1 = c(1,1,1,2,2,2,3,3,3,4,4,4),
                 grp2 = c(1,2,3,3,4,5,6,7,8,6,9,10))

#> df
#   grp1 grp2
#1            


        

Answer 1

Based on https://stackoverflow.com/a/35773701/2152245, I used a different implementation of igraph because I already had an adjacency matrix of sf polygons from st_intersects():

library(igraph)
library(sf)
# Use example data
nc <- st_read(system.file("shape/nc.shp", package="sf"))
nc <- nc[-sample(1:nrow(nc),nrow(nc)*.75),] #drop some polygons
# Find intersetions
b <- st_intersects(nc, sparse = F)
g  <- graph.adjacency(b)
clu <- components(g)
gr <- groups(clu)
# Quick loop to assign the groups
for(i in 1:nrow(nc)){
    for(j in 1:length(gr)){
      if(i %in% gr[[j]]){
        nc[i,'group'] <- j
      }
    }
  }
# Make a new sfc object
nc_un <- group_by(nc, group) %>% 
    summarize(BIR74 = mean(BIR74), do_union = TRUE)
plot(nc_un['BIR74'])