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#' aggregate an \code{sf} object
#'
#' aggregate an \code{sf} object, possibly union-ing geometries
#'
#' @note Does not work using the formula notation involving \code{~} defined in \link[stats]{aggregate}.
#'
#' @param x object of class \link{sf}
#' @param by either a list of grouping vectors with length equal to \code{nrow(x)} (see \link[stats]{aggregate}), or an object of class \code{sf} or \code{sfc} with geometries that are used to generate groupings, using the binary predicate specified by the argument \code{join}
#' @param FUN function passed on to \link[stats]{aggregate}, in case \code{ids} was specified and attributes need to be grouped
#' @param ... arguments passed on to \code{FUN}
#' @param do_union logical; should grouped geometries be unioned using \link{st_union}? See details.
#' @param simplify logical; see \link[stats]{aggregate}
#' @param join logical spatial predicate function to use if \code{by} is a simple features object or geometry; see \link{st_join}
#' @return an \code{sf} object with aggregated attributes and geometries; additional grouping variables having the names of \code{names(ids)} or are named \code{Group.i} for \code{ids[[i]]}; see \link[stats]{aggregate}.
#' @details In case \code{do_union} is \code{FALSE}, \code{aggregate} will simply combine geometries using \link{c.sfg}. When polygons sharing a boundary are combined, this leads to geometries that are invalid; see \url{https://github.com/r-spatial/sf/issues/681}.
#' @aliases aggregate
#' @examples
#' m1 = cbind(c(0, 0, 1, 0), c(0, 1, 1, 0))
#' m2 = cbind(c(0, 1, 1, 0), c(0, 0, 1, 0))
#' pol = st_sfc(st_polygon(list(m1)), st_polygon(list(m2)))
#' set.seed(1985)
#' d = data.frame(matrix(runif(15), ncol = 3))
#' p = st_as_sf(x = d, coords = 1:2)
#' plot(pol)
#' plot(p, add = TRUE)
#' (p_ag1 = aggregate(p, pol, mean))
#' plot(p_ag1) # geometry same as pol
#' # works when x overlaps multiple objects in 'by':
#' p_buff = st_buffer(p, 0.2)
#' plot(p_buff, add = TRUE)
#' (p_ag2 = aggregate(p_buff, pol, mean)) # increased mean of second
#' # with non-matching features
#' m3 = cbind(c(0, 0, -0.1, 0), c(0, 0.1, 0.1, 0))
#' pol = st_sfc(st_polygon(list(m3)), st_polygon(list(m1)), st_polygon(list(m2)))
#' (p_ag3 = aggregate(p, pol, mean))
#' plot(p_ag3)
#' # In case we need to pass an argument to the join function:
#' (p_ag4 = aggregate(p, pol, mean,
#' join = function(x, y) st_is_within_distance(x, y, dist = 0.3)))
#' @export
aggregate.sf = function(x, by, FUN, ..., do_union = TRUE, simplify = TRUE,
join = st_intersects) {
if (inherits(by, "sf") || inherits(by, "sfc")) {
if (inherits(by, "sfc"))
by = st_sf(by)
i = join(st_geometry(by), st_geometry(x))
st_geometry(x) = NULL
# dispatch to stats::aggregate:
a = aggregate(x[unlist(i), , drop = FALSE],
list(rep(seq_len(nrow(by)), lengths(i))), FUN, ...)
nrow_diff = nrow(by) - nrow(a)
if(nrow_diff > 0) {
a_na = a[rep(NA, nrow(by)),] # 'top-up' missing rows
a_na[a$Group.1,] = a
a = a_na
}
a$Group.1 = NULL # remove
row.names(a) = row.names(by)
st_set_geometry(a, st_geometry(by))
} else {
crs = st_crs(x)
lst = lapply(split(st_geometry(x), by), function(y) do.call(c, y))
geom = do.call(st_sfc, lst[!sapply(lst, is.null)])
if (do_union)
geom = st_union(st_set_precision(geom, st_precision(x)), by_feature = TRUE)
st_geometry(x) = NULL
x = aggregate(x, by, FUN, ..., simplify = simplify)
st_geometry(x) = geom # coerces to sf
st_crs(x) = crs
# now set agr:
geoms = which(vapply(x, function(vr) inherits(vr, "sfc"), TRUE))
agr_names = names(x)[-geoms]
agr = rep("aggregate", length(agr_names))
names(agr) = agr_names
# which ones are identity variables?
n = if (!is.null(names(by)))
names(by)
else
paste0("Group.", seq_along(by))
agr[n] = "identity"
st_agr(x) = agr
x
}
}
#' Areal-weighted interpolation of polygon data
#'
#' Areal-weighted interpolation of polygon data
#' @name interpolate_aw
#' @param x object of class \code{sf}, for which we want to aggregate attributes
#' @param to object of class \code{sf} or \code{sfc}, with the target geometries
#' @param extensive logical; if TRUE, the attribute variables are assumed to be spatially extensive (like population) and the sum is preserved, otherwise, spatially intensive (like population density) and the mean is preserved.
#' @param ... ignored
#' @param keep_NA logical; if \code{TRUE}, return all features in \code{to}, if \code{FALSE} return only those with non-NA values (but with \code{row.names} the index corresponding to the feature in \code{to})
#' @examples
#' nc = st_read(system.file("shape/nc.shp", package="sf"))
#' g = st_make_grid(nc, n = c(10, 5))
#' a1 = st_interpolate_aw(nc["BIR74"], g, extensive = FALSE)
#' sum(a1$BIR74) / sum(nc$BIR74) # not close to one: property is assumed spatially intensive
#' a2 = st_interpolate_aw(nc["BIR74"], g, extensive = TRUE)
#' # verify mass preservation (pycnophylactic) property:
#' sum(a2$BIR74) / sum(nc$BIR74)
#' a1$intensive = a1$BIR74
#' a1$extensive = a2$BIR74
#' \donttest{plot(a1[c("intensive", "extensive")], key.pos = 4)}
#' @export
st_interpolate_aw = function(x, to, extensive, ...) UseMethod("st_interpolate_aw")
#' @export
#' @name interpolate_aw
st_interpolate_aw.sf = function(x, to, extensive, ..., keep_NA = FALSE) {
if (!inherits(to, "sf") && !inherits(to, "sfc")) {
to <- try(st_as_sf(to))
if (inherits(to, "try-error"))
stop("st_interpolate_aw requires geometries in argument to")
}
if (! all_constant(x))
warning("st_interpolate_aw assumes attributes are constant or uniform over areas of x")
i = st_intersection(st_geometry(x), st_geometry(to), dimensions = "polygon")
idx = attr(i, "idx")
# https://stackoverflow.com/questions/57767022/how-do-you-use-st-interpolate-aw-with-polygon-layers-that-legitimately-include-p
gc = which(st_is(i, "GEOMETRYCOLLECTION"))
i[gc] = st_collection_extract(i[gc], "POLYGON")
two_d = which(st_dimension(i) == 2)
i[two_d] = st_cast(i[two_d], "MULTIPOLYGON")
x_st = st_set_geometry(x, NULL)[idx[,1],, drop=FALSE] # create st table, remove geom
if (any(!sapply(x_st, is.numeric)))
stop("x contains non-numeric column(s)")
area_i = try(st_area(i), silent = TRUE)
if (inherits(area_i, "try-error"))
area_i <- st_area(st_make_valid(i)) # work-around for https://github.com/r-spatial/sf/issues/1810
x_st$...area_st = unclass(area_i)
x_st = if (extensive) {
# compute area_s:
x_st$...area_s = unclass(st_area(x))[idx[,1]]
lapply(x_st, function(v) v * x_st$...area_st / x_st$...area_s)
} else {
# compute area_t:
target = sapply(split(area_i, idx[, 2]), sum) # and not st_area(to)?
df = data.frame(area = target, idx = as.integer(names(target)))
x_st$...area_t = merge(data.frame(idx = idx[,2]), df)$area
lapply(x_st, function(v) v * x_st$...area_st / x_st$...area_t)
}
x_st = aggregate(x_st, list(idx[,2]), sum)
df = if (keep_NA) {
ix = rep(NA_integer_, length(to))
ix[x_st$Group.1] = seq_along(x_st$Group.1)
st_sf(x_st[ix,], geometry = st_geometry(to))
} else
st_sf(x_st, geometry = st_geometry(to)[x_st$Group.1], row.names = x_st$Group.1)
# clean up:
df$...area_t = df$...area_st = df$...area_s = df$Group.1 = NULL
st_set_agr(df, "aggregate")
}
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