快速计算R中多边形列表内的点的方法
我有两个数据集,一个有超过1300万个矩形多边形(4个lat lng点集),另一个有10000个点涉及该位置的价格快速计算R中多边形列表内的点的方法,r,sp,point-in-polygon,R,Sp,Point In Polygon,我有两个数据集,一个有超过1300万个矩形多边形(4个lat lng点集),另一个有10000个点涉及该位置的价格 > polygons id pol_lat pol_lng 1: 148 -4.250236,-4.250236,-4.254640,-4.254640 -49.94628,-49.94494,-49.94494,-49.94628 2
> polygons
id pol_lat pol_lng
1: 148 -4.250236,-4.250236,-4.254640,-4.254640 -49.94628,-49.94494,-49.94494,-49.94628
2: 149 -4.254640,-4.254640,-5.361601,-5.361601 -49.94494,-49.07906,-49.07906,-49.94494
3: 150 -5.361601,-5.361601,-5.212208,-5.212208 -49.07906,-49.04469,-49.04469,-49.07906
4: 151 -5.212208,-5.212208,-5.002878,-5.002878 -49.04469,-48.48664,-48.48664,-49.04469
5: 152 -5.002878,-5.002878,-5.080018,-5.080018 -48.48664,-48.43699,-48.43699,-48.48664
6: 153 -5.080018,-5.080018,-5.079819,-5.079819 -48.43699,-48.42480,-48.42480,-48.43699
7: 154 -5.079819,-5.079819,-5.155606,-5.155606 -48.42480,-47.53891,-47.53891,-48.42480
8: 155 -5.155606,-5.155606,-4.954156,-4.954156 -47.53891,-47.50354,-47.50354,-47.53891
9: 156 -4.954156,-4.954156,-3.675864,-3.675864 -47.50354,-45.39022,-45.39022,-47.50354
10: 157 -3.675864,-3.675864,-3.706356,-3.706356 -45.39022,-45.30724,-45.30724,-45.39022
11: 158 -3.706356,-3.706356,-3.705801,-3.705801 -45.30724,-45.30722,-45.30722,-45.30724
> points
longitude latitude price
1: -47.50308 -4.953936 3.0616
2: -47.50308 -4.953936 3.2070
3: -47.50308 -4.953936 3.0630
4: -47.50308 -4.953936 3.0603
5: -47.50308 -4.953936 3.0460
6: -47.50308 -4.953936 2.9900
7: -49.07035 -5.283658 3.3130
8: -49.08054 -5.347284 3.3900
9: -49.08054 -5.347284 3.3620
10: -49.21726 -5.338270 3.3900
11: -49.08050 -5.347255 3.4000
12: -49.08042 -5.347248 3.3220
13: -49.08190 -5.359508 3.3130
14: -49.08046 -5.347277 3.3560
我想为每个多边形生成适合每个多边形的所有点的平均价格
现在我正在使用sp::point.in.polygon
获取适合给定多边形的所有点的索引,然后获取其平均价格
w <- lapply(1:nrow(polygons),
function(tt) {
ind <- point.in.polygon(points$latitude, points$longitude,
polygons$pol_lat[[tt]], polygons$pol_lng[[tt]]) > 0
med <- mean(points$price[ind])
return(med)
}
)
> unlist(w)
[1] NaN 3.361857 3.313000 NaN NaN NaN NaN NaN 3.071317 NaN NaN
如果您的“多边形”始终是矩形如示例中所示,则可以使用四叉树空间索引(如packageSearchTrees
中实现的),以提高识别每个多边形中哪些点的速度
由于空间索引所允许的“比较”次数越少,数据集中的点数越多,因此它可以大大提高速度
例如:
library(SearchTrees)
library(magrittr)
# Create a "beefier" test dataset based on your data: 14000 pts
# over 45000 polygons
for (i in 1:10) points <- rbind(points, points + runif(length(points)))
for (i in 1:12) polygons <- rbind(polygons, polygons)
# Compute limits of the polygons
min_xs <- lapply(polygons$pol_lng , min) %>% unlist()
max_xs <- lapply(polygons$pol_lng , max) %>% unlist()
min_ys <- lapply(polygons$pol_lat , min) %>% unlist()
max_ys <- lapply(polygons$pol_lat, max) %>% unlist()
xlims <- cbind(min_xs, max_xs)
ylims <- cbind(min_ys, max_ys)
# Create the quadtree
tree = SearchTrees::createTree(cbind(points[1],points[2]))
#☻ extract averages, looping over polygons ----
t1 <- Sys.time()
w <- lapply(1:nrow(polygons),
function(tt) {
ind <- SearchTrees::rectLookup(
tree,
xlims = xlims[tt,],
ylims = ylims[tt,]))
mean(points$price[ind])
})
Sys.time() - t1
整体速度的提高将取决于点在空间范围内以及相对于多边形的“聚集”方式
如果多边形不是矩形,也可以考虑利用此方法,方法是首先提取每个多边形的bbox中包含的点,然后使用更标准的方法查找多边形“内部”的点
也认为任务是并行的,因此可以通过使用<代码> PROACH 或<代码> PARLAPEP 方法来改进性能。p>
嗯 可能会有帮助:我已经访问了第二个链接,但是
ptinpoly
并没有提供多少速度提升。将查看第一个链接中的答案是否有帮助。感谢您不是空间统计方面的专家,但是您的lappy正在对所有多边形进行迭代,如果点的数量远小于多边形的数量(在您的案例中显然是这样),那么这可能会导致效率低下。您是否尝试过在点上迭代,然后查看它是否属于多边形?这种方法的好处是,如果多边形是一个分区,那么一旦你找到了一个点所属的多边形,你就可以停止寻找其他点,继续寻找下一个点。现在有点傻了,因为没有考虑它。谢谢@mbironMy多边形可以有重叠区域。我已经只检查了离每个点最近的多边形。反转循环,也就是在点上迭代,这项技巧帮助很大。奇怪的是它的速度是4倍,而不是10倍。尽管如此,还是有了很大的进步
library(SearchTrees)
library(magrittr)
# Create a "beefier" test dataset based on your data: 14000 pts
# over 45000 polygons
for (i in 1:10) points <- rbind(points, points + runif(length(points)))
for (i in 1:12) polygons <- rbind(polygons, polygons)
# Compute limits of the polygons
min_xs <- lapply(polygons$pol_lng , min) %>% unlist()
max_xs <- lapply(polygons$pol_lng , max) %>% unlist()
min_ys <- lapply(polygons$pol_lat , min) %>% unlist()
max_ys <- lapply(polygons$pol_lat, max) %>% unlist()
xlims <- cbind(min_xs, max_xs)
ylims <- cbind(min_ys, max_ys)
# Create the quadtree
tree = SearchTrees::createTree(cbind(points[1],points[2]))
#☻ extract averages, looping over polygons ----
t1 <- Sys.time()
w <- lapply(1:nrow(polygons),
function(tt) {
ind <- SearchTrees::rectLookup(
tree,
xlims = xlims[tt,],
ylims = ylims[tt,]))
mean(points$price[ind])
})
Sys.time() - t1
w1 <- unlist(w)
t1 <- Sys.time()
w <- lapply(1:nrow(polygons),
function(tt) {
ind <- sp::point.in.polygon(points$latitude, points$longitude,
polygons$pol_lat[[tt]], polygons$pol_lng[[tt]]) > 0
med <- mean(points$price[ind])
return(med)
}
)
Sys.time() - t1
w2 <- unlist(w)
> all.equal(w1, w2)
[1] TRUE