Identify contiguous sets of units and numbers each set. Can be extended to repeat the procedure within a subgeography.
check_contiguity(adj, group)
cct(adj, group)
ccm(adj, group)adjacency list
array of group identifiers. Typically district numbers or county names. Defaults to 1 if no input is provided, checking that the adjacency list itself is one connected component.
tibble with contiguity indicators. Each row is the units of adj. Columns include
group Values of the inputted group argument. If group is not specified, then all values
will be 1.
component A number for each contiguous set of units within a group. If all units within a
group are contiguous, all values are 1. If there are two sets, each discontiguous with
the other, the larger one will be numbered 1 and the smaller one will be numbered as 2.
Given a zero-indexed adjacency list and an array of group identifiers, this
returns a tibble which identifies the connected components. The three columns
are group for the inputted group, group_number which uniquely identifies each
group as a positive integer, and component which identifies the connected
component number for each corresponding entry of adjacency and group. If everything
is connected within the group, then each element of component will be 1.
Otherwise, the largest component is given the value 1, the next largest 2,
and so on.
If nothing is provided to group, it will default to a vector of ones, checking if the adjacency graph is connected.
cct() is shorthand for creating a table of the component values. If everything
is connected within each group, it returns a value of 1. In general, it returns
a frequency table of components.
ccm() is shorthand for getting the maximum component value. It returns the
maximum number of components that a group is broken into.
This returns 1 if each group is connected. #'
data(checkerboard)
adj <- adjacency(checkerboard)
#> Warning: Planarizing skipped. `x` missing CRS.
# These each indicate the graph is connected.
check_contiguity(adj) # all contiguous
#> # A tibble: 64 × 3
#> group group_number component
#> <int> <int> <int>
#> 1 1 1 1
#> 2 1 1 1
#> 3 1 1 1
#> 4 1 1 1
#> 5 1 1 1
#> 6 1 1 1
#> 7 1 1 1
#> 8 1 1 1
#> 9 1 1 1
#> 10 1 1 1
#> # ℹ 54 more rows
# If there are two discontiguous groups, there will be 2 values of `component`
cct(adj)
#>
#> 1
#> 64
ccm(adj)
#> [1] 1