基于@data槽中的字段，合并空间多边形数据框中的多边形。

Question

我不太擅长R语言和空间分析。我正在寻找一种方法，根据数据框中的字段，将空间多边形数据框内的多边形组合起来：类似于dplyr的“group_by”功能，但是用于spdf。我不确定合并、连接或组合这些词是否正确，但我希望我的需求很清楚。

library(sp)

#coordinates:
xy1 = cbind(c(1,2,2,1),c(1,1,2,2))
xy2 = cbind(c(2,3,3,2),c(1,1,2,2))
xy3 = cbind(c(1,2,2,1),c(2,2,3,3))
xy4 = cbind(c(2,3,3,2),c(2,2,3,3))

#polygons:
p1 = Polygon(xy1)
ps1 = Polygons(list(p1),ID = "a")
p2 = Polygon(xy2)
ps2 = Polygons(list(p2),ID = "b")
p3 = Polygon(xy3)
ps3 = Polygons(list(p3),ID = "c")
p4 = Polygon(xy4)
ps4 = Polygons(list(p4),ID = "d")

#spatial polygons:
sps_m = SpatialPolygons(list(ps1,ps2,ps3,ps4))

#dataframe:
data_m = data.frame(dt = c("Group A","Group B","Group A","Group C"),row.names = c("a","b","c","d"))

#spatial polygons dataframe:
spdf_m = SpatialPolygonsDataFrame(sps_m,data_m)

#plot spdf:
plot(spdf_m)

- Claudio Paladini

---

听起来你想要一个溶解函数，这个函数是gUnaryUnion()。冒昧地说，我最近写了一篇关于多边形溶解的文章：https://philmikejones.me/post/2015-09-03-dissolve-polygons-in-r/ - Phil

哈哈，是的，谢谢。同时我也找到了：https://philmikejones.wordpress.com/2015/09/03/dissolve-polygons-in-r/ - Claudio Paladini

还有来自raster库的aggregate()：https://www.rdocumentation.org/packages/raster/versions/2.6-7/topics/aggregate - Claudio Paladini

@Phil 这是一篇很棒的文章，而且你更新了它以符合 sf 的方式。我非常赞同你的观点！ - Fitzroy Hogsflesh

Answer 1

正确的术语来描述将多个面合并为一个的行为似乎是“dissolving”或“aggregating”。

在我的工作中，使用的功能是raster包中的aggregate()。

library(sp)
library(raster)

#coordinates:
xy1 = cbind(c(1,2,2,1),c(1,1,2,2))
xy2 = cbind(c(2,3,3,2),c(1,1,2,2))
xy3 = cbind(c(1,2,2,1),c(2,2,3,3))
xy4 = cbind(c(2,3,3,2),c(2,2,3,3))

#polygons:
p1 = Polygon(xy1)
ps1 = Polygons(list(p1),ID = "a")
p2 = Polygon(xy2)
ps2 = Polygons(list(p2),ID = "b")
p3 = Polygon(xy3)
ps3 = Polygons(list(p3),ID = "c")
p4 = Polygon(xy4)
ps4 = Polygons(list(p4),ID = "d")

#spatial polygons:
sps_m = SpatialPolygons(list(ps1,ps2,ps3,ps4))

#dataframe:
data_m = data.frame(dt = c("Group A","Group B","Group A","Group C"),row.names = c("a","b","c","d"))

#spatial polygons dataframe:
spdf_m = SpatialPolygonsDataFrame(sps_m,data_m)

groups = aggregate(spdf_m, by = "dt")

#plot spdf:
plot(spdf_m)
plot(groups)

- Claudio Paladini