Select features by size

Select the largest or smallest polygons or lines in a SpatVector, optionally providing a maximum number of selected features, filtering by a size threshold, dissolving adjacent features, and/or splitting multipart features into single parts.

Usage

# S4 method for class 'SpatVector'
selectSize(x, n=Inf, largest=TRUE, threshold=NULL,
           dissolve=FALSE, singleparts=TRUE)

Arguments

x: SpatVector of polygons or lines
n: optional integer value (default Inf) indicating the maximum number of largest or smallest features to select (if they pass the optional threshold)
largest: if TRUE (default) select the largest feature(s), otherwise the smallest
threshold: optional size threshold (area in square meters for polygons, length in meters for lines) above which (if largest=TRUE or below which (if largest=FALSE features should be selected
dissolve: if TRUE, aggregate features before selection. Default FALSE
singleparts: if TRUE (default), split multipart features into individual parts before selection

Details

Polygon size is calculated using expanse; line size is calculated using perim. The threshold is applied before selecting the requested number of features. If fewer than n features satisfy the threshold, only qualifying features are returned.

If dissolve=TRUE, features are aggregated before size calculation. If singleparts=TRUE, multipart features are disaggregated before size calculation.

Value

SpatVector containing the selected features.

Author

A. Márcia Barbosa

Examples

f <- system.file("ex/lux.shp", package="terra")
v <- vect(f)

# Select the five largest polygons
large5 <- selectSize(v, n=5)

# Select the three smallest polygons
small3 <- selectSize(v, n=3, largest=FALSE)

# Select up to 4 largest polygons satisfying a given minimum area
large <- selectSize(v, n=4, threshold=260e+6)

if (FALSE) { # \dontrun{
plot(v)
polys(large5, col="red")
polys(small3, col="blue")
polys(large, col="gold", density=50)
} # }