Convert to an edge lines object — st_as

Given geometry and neighbor and weights lists, create an edge list sf object.

Usage

st_as_edges(x, nb, wt)

# S3 method for sf
st_as_edges(x, nb, wt)

# S3 method for sfc
st_as_edges(x, nb, wt)

Arguments

x: object of class sf or sfc.
nb: a neighbor list. If x is class sf, the unquote named of the column. If x is class sfc, an object of class nb as created from st_contiguity().
wt: optional. A weights list as generated by st_weights(). . If x is class sf, the unquote named of the column. If x is class sfc, the weights list itself.

Value

Returns an sf object with edges represented as a LINESTRING.

from: node index. This is the row position of x.
to: node index. This is the neighbor value stored in nb.
i: node index. This is the row position of x.
j: node index. This is the neighbor value stored in nb.
wt: the weight value of j stored in wt.

Details

Creating an edge list creates a column for each i position and j between an observation and their neighbors. You can recreate these values by expanding the nb and wt list columns.

library(magrittr)
guerry_nb %>%
  tibble::as_tibble() %>%
  dplyr::select(nb, wt) %>%
  dplyr::mutate(i = dplyr::row_number(), .before = 1) %>%
  tidyr::unnest(c(nb, wt))
#> # A tibble: 420 x 3
#>        i    nb    wt
#>    <int> <int> <dbl>
#>  1     1    36 0.25 
#>  2     1    37 0.25 
#>  3     1    67 0.25 
#>  4     1    69 0.25 
#>  5     2     7 0.167
#>  6     2    49 0.167
#>  7     2    57 0.167
#>  8     2    58 0.167
#>  9     2    73 0.167
#> 10     2    76 0.167
#> # i 410 more rows

Examples


if (requireNamespace("dplyr", quietly = TRUE)) {

library(magrittr)
guerry %>%
  dplyr::mutate(nb = st_contiguity(geometry),
         wt = st_weights(nb)) %>%
  st_as_edges(nb, wt)

}
#> Simple feature collection with 420 features and 5 fields
#> Geometry type: LINESTRING
#> Dimension:     XY
#> Bounding box:  xmin: 143129.7 ymin: 1735692 xmax: 983300.8 ymax: 2615768
#> CRS:           NA
#> First 10 features:
#>    from to i  j        wt                       geometry
#> 1     1 36 1 36 0.2500000 LINESTRING (827911.9 212290...
#> 2     1 37 1 37 0.2500000 LINESTRING (827911.9 212290...
#> 3     1 67 1 67 0.2500000 LINESTRING (827911.9 212290...
#> 4     1 69 1 69 0.2500000 LINESTRING (827911.9 212290...
#> 5     2  7 2  7 0.1666667 LINESTRING (691725.7 249605...
#> 6     2 49 2 49 0.1666667 LINESTRING (691725.7 249605...
#> 7     2 57 2 57 0.1666667 LINESTRING (691725.7 249605...
#> 8     2 58 2 58 0.1666667 LINESTRING (691725.7 249605...
#> 9     2 73 2 73 0.1666667 LINESTRING (691725.7 249605...
#> 10    2 76 2 76 0.1666667 LINESTRING (691725.7 249605...