dissolve attributes of a vector and aggregate its table

Source: R/dissolve_vect.R

Perform a "dissolve" (a.k.a. aggregation) operation on a vector object according to a grouping variable, also aggregate values of the attribute table for all other columns over the same grouping variable.

Aggregation of factor or character columns is done as follows: - If all polygons that are aggregated to a common dissolved polygon had the same value for the column, then the value is preserved; - If polygons had different values, the column takes the value "variable" or NA (depending on var_as_NA )

Aggregation of factor or character columns is done as follows:

- If the column represent a "quantity" (e.g., Population), the value for each
  dissolved is computed as the sum of the values of the original
  polygons belonging to it;

TODO - If the column represents a "density" (e.g., ton ha-1), the value for each dissolved is computed as the average of the values of the original polygons belonging to it, weighted by their area; STILL TO BE IMPLEMENTED ! CURRENTLY ALL COLUMNS ARE COMPUTED SIMPLY AS THE SUM !!!!

dissolve_vect(in_vect, dissolve_var, var_as_NA = FALSE,
  out_file = NULL, out_type = "vectobject", overwrite = FALSE,
  verbose = TRUE)

Arguments

in_vect

Either a R vector object (sf or sp), or the path to a valid vector file
dissolve_var

character column of the attribute table of in_vect on to which the dissolve has to be performed.
var_as_NA

logical TO BE DESCRIBED - see examples for now!!!, Default: FALSE
out_file

character output file name
out_type

character ["vectfile" | "vectobject"] If "vectfile", and out_file is not NULL, the function returns the name of the saved shapefile. Otherwise, it returns the reprojected vector object, with the format specified by out_class, Default: 'vectobject'
overwrite

logical if TRUE, output file will be overwritten if existing, Default: FALSE
verbose

logical if TRUE, provide messages on processing, Default: TRUE

Value

an *sf object. The object is also saved to disk as a shapefile if out_file is provided

Examples


 library(sprawl.data)
 library(maps)

 in_vect    <- get(load(system.file("extdata/shapes","poly_lomb.RData",
    package = "sprawl.data")))
 plot_vect(in_vect, fill_var = "NAME_2")
#> Coordinate system already present. Adding new coordinate system, which will replace the existing one.
#> Coordinate system already present. Adding new coordinate system, which will replace the existing one.
 plot_vect(in_vect, fill_var = "population", palette_name = "RdYlGn")
#> Coordinate system already present. Adding new coordinate system, which will replace the existing one.
#> Coordinate system already present. Adding new coordinate system, which will replace the existing one.

 # Dissolve the vector to provinces
 diss <- dissolve_vect(in_vect, "NAME_2")
#> Joining, by = "NAME_2"
#> Warning: Column `NAME_2` joining factor and character vector, coercing into character vector
 diss
#> Simple feature collection with 12 features and 4 fields
#> geometry type:  GEOMETRY
#> dimension:      XY
#> bbox:           xmin: 8.49941 ymin: 44.6809 xmax: 11.42868 ymax: 46.63806
#> epsg (SRID):    4326
#> proj4string:    +proj=longlat +datum=WGS84 +no_defs
#> # A tibble: 12 x 5
#>    NAME_2     NAME_1  year   population                                 geometry
#>    <chr>      <fct>   <chr>       <dbl>                           <GEOMETRY [°]>
#>  1 Bergamo    Lombar… varia…         28 POLYGON ((10.10427 46.08951, 10.10582 4…
#>  2 Brescia    Lombar… varia…         25 POLYGON ((10.50012 46.33554, 10.51088 4…
#>  3 Como       Lombar… varia…         39 POLYGON ((9.295499 46.23737, 9.302701 4…
#>  4 Cremona    Lombar… varia…         38 POLYGON ((9.551826 45.46125, 9.57864 45…
#>  5 Lecco      Lombar… varia…         41 POLYGON ((9.491518 46.07167, 9.49338 46…
#>  6 Lodi       Lombar… varia…        116 POLYGON ((9.532625 45.16629, 9.529924 4…
#>  7 Mantua     Lombar… varia…         18 POLYGON ((10.69031 45.42357, 10.69465 4…
#>  8 Milano     Lombar… varia…         16 POLYGON ((8.955621 45.6264, 8.956942 45…
#>  9 Monza and… Lombar… varia…         23 POLYGON ((9.260717 45.74068, 9.261759 4…
#> 10 Pavia      Lombar… varia…         14 MULTIPOLYGON (((8.814569 45.01818, 8.81…
#> 11 Sondrio    Lombar… varia…         51 POLYGON ((10.25107 46.6226, 10.2514 46.…
#> 12 Varese     Lombar… varia…         13 POLYGON ((8.772502 46.10313, 8.774683 4…

 plot_vect(diss, fill_var = "NAME_2")
#> Coordinate system already present. Adding new coordinate system, which will replace the existing one.
#> Coordinate system already present. Adding new coordinate system, which will replace the existing one.
 provinces <- get_boundaries("ITA", 2)
#> get_boundaries --> Downloading data for: "ITA", Level: 2

 plot_vect(diss, fill_var = "population", palette_name = "RdYlBu",
         leg_position = "bottom")
#> Coordinate system already present. Adding new coordinate system, which will replace the existing one.
#> Coordinate system already present. Adding new coordinate system, which will replace the existing one.