Minimum spanning trees

[francescmolne]

Hi, is it possible to create minimum spanning trees (mst() function in igraph)?
Many thanks!

[idshklein]

I think so, example added below:

library(tidyverse)
#> Warning: package 'tibble' was built under R version 4.0.5
#> Warning: package 'tidyr' was built under R version 4.0.5
#> Warning: package 'readr' was built under R version 4.0.3
#> Warning: package 'dplyr' was built under R version 4.0.3
library(sf)
#> Warning: package 'sf' was built under R version 4.0.5
#> Linking to GEOS 3.9.0, GDAL 3.2.1, PROJ 7.2.1
library(sfnetworks)
#> Warning: package 'sfnetworks' was built under R version 4.0.5
#> Registered S3 method overwritten by 'spatstat.geom':
#>   method     from
#>   print.boxx cli
library(igraph)
#> Warning: package 'igraph' was built under R version 4.0.3
#> 
#> Attaching package: 'igraph'
#> The following objects are masked from 'package:dplyr':
#> 
#>     as_data_frame, groups, union
#> The following objects are masked from 'package:purrr':
#> 
#>     compose, simplify
#> The following object is masked from 'package:tidyr':
#> 
#>     crossing
#> The following object is masked from 'package:tibble':
#> 
#>     as_data_frame
#> The following objects are masked from 'package:stats':
#> 
#>     decompose, spectrum
#> The following object is masked from 'package:base':
#> 
#>     union
library(tidygraph)
#> 
#> Attaching package: 'tidygraph'
#> The following object is masked from 'package:igraph':
#> 
#>     groups
#> The following object is masked from 'package:stats':
#> 
#>     filter
net <- roxel %>% 
  st_transform(5683) %>% 
  as_sfnetwork() %>% 
  activate(edges) %>% 
  mutate(rn = row_number())
#> old-style crs object detected; please recreate object with a recent sf::st_crs()
minst <- mst(net) %>% 
  as_sfnetwork() %>% 
  activate(edges) %>% 
  left_join(net %>% 
              activate(edges) %>% 
              st_as_sf(),by = "rn") %>% 
  st_as_sf() 
#> Checking if spatial network structure is valid...
#> Spatial network structure is valid
net %>% 
  activate(nodes) %>% 
  st_as_sf() %>% 
  ggplot() + 
  geom_sf() + 
  geom_sf(data = net %>% 
            activate(edges) %>% 
            st_as_sf()) + 
  geom_sf(data = minst, color = "red")

^{Created on 2022-02-02 by the reprex package (v0.3.0)}

[luukvdmeer]

As of sfnetworks v1.0

To create a spatial minimum spanning tree only from a set of spatial points:

library(sfnetworks)

# Using here the mozart dataset of point locations
mst = as_sfnetwork(mozart, "mst")

To create a spatial minimum spanning tree of an existing network:

library(sfnetworks)
library(tidygraph)

as_sfnetwork(roxel) |>
  activate(edges) |>
  mutate(length = edge_length()) |>
  convert(to_minimum_spanning_tree, weights = length)