Join the points of each group into a line

Returns one linestring through the points that share each label of by, taking the points in row order. With by = NULL, ga_make_line_agg() joins every point into a single line.

Usage

ga_make_line_agg(points, by = NULL)

Arguments

points

a GeoArrow point array

by

a character vector, numeric vector, or Arrow array with one label per point, or NULL for a single line

Value

a GeoArrow linestring array with one element per label of by

Details

ga_make_line_agg() groups the rows the way ga_collect_agg() does. It accepts an unsorted by, treats NA as a label like any other, and orders the lines by where each label first appears, so you can name the lines with unique(by).

ga_make_line_agg() skips null and empty points, and returns a null line for a group with fewer than two points left. It keeps the z and m values and the CRS of points. This is the aggregate form of PostGIS ST_MakeLine(); use ga_make_line() to join pairs of points instead.

See also

Other construct: ga_linestring(), ga_make_envelope(), ga_make_grid(), ga_make_line(), ga_make_polygon(), ga_multilinestring(), ga_multipoint(), ga_multipolygon(), ga_point(), ga_polygon()

Examples

pts <- ga_point(c(0, 1, 2, 10, 11), c(0, 1, 0, 5, 5))
lines <- ga_make_line_agg(pts, by = c("a", "a", "a", "b", "b"))
sf::st_as_sfc(geoarrow::as_geoarrow_vctr(lines))
#> Geometry set for 2 features 
#> Geometry type: LINESTRING
#> Dimension:     XY
#> Bounding box:  xmin: 0 ymin: 0 xmax: 11 ymax: 5
#> CRS:           NA
#> LINESTRING (0 0, 1 1, 2 0)
#> LINESTRING (10 5, 11 5)

as.vector(ga_length_euclidean(lines))
#> [1] 2.828427 1.000000