问题描述
如何仅接收相交的SpatialLines的差异的SpatialLines列表?
How to receive a list of SpatialLines of the differences of the intersecting SpatialLines only?
创建SpatialLines:
create SpatialLines:
#from the sp vignette:
l1 = cbind(c(1,2,3,4),c(3,2,2,4))
rownames(l1) = letters[1:4]
l2 = cbind(c(2,2,3,3),c(3,2,2,5))
rownames(l2) = letters[1:4]
l3 = cbind(c(1,2,3,4),c(1,2,2,1))
rownames(l3) = letters[1:4]
Sl1 = Line(l1)
Sl2 = Line(l2)
Sl3 = Line(l3)
Ll1 = Lines(list(Sl1), ID="a")
Ll2 = Lines(list(Sl2), ID="b")
Ll3 = Lines(list(Sl3), ID="c")
Sl = SpatialLines(list(Ll1,Ll2,Ll3))
结果SpatialLines("Sl")显示相交和差异.可以通过以下方式获得列表中所有SpatialLines的差异:
resulting SpatialLines ("Sl") show intersections and differences.Receiving the differences of all SpatialLines of the list can be achieved like this:
C = combn(1:length(Sl),2)
C2 = cbind(C,C[2:1,])
MyDiffs = apply(C2, 2, function(x){gDifference(Sl[x[1]], Sl[x[2]])})
仅查找相交的SpatialLines的差异.我在考虑类似条件 gIntersect = TRUE 然后应用 gDifference().但是，我找不到在R中执行此操作的方法.也许有一个更聪明的解决方案...
Looking for the differences of the intersecting SpatialLines only.I was thinking about something like if the condition gIntersect=TRUE then apply gDifference(). However, I can´t find a way to do that in R.Maybe there´s a smarter solution...
修改: bogdata 的答案有效，但是所有差异都出现两次.以删除下部三角形部分的方式来处理矩阵会导致以下结果:保留一些加倍的差，而删除其他的差.
The answer of bogdata works, but all differences appear twice.Manipulating the matrix in a way that the lower triangular part get removed led to the result that some doubled differences are kept while others get removed.
library("reshape2")
# compute intersection matrix by ID
intersections <- gIntersects(Sl, byid=TRUE)
# set lower triangular part of matrix NA
intersections[lower.tri(intersections, diag = TRUE)] <- NA
# melt matrix into edge list (+remove NA)
intersections <- melt(intersections, na.rm=TRUE)
# compute differences
MyDiffs = apply(intersections, 1, function(x){gDifference(Sl[x[1]], Sl[x[2]])})
有什么建议吗?
推荐答案
只需在 byid = T 和 melt 函数中使用 gIntersects reshape2 :
library("reshape2")
# compute intersection matrix by ID
intersections <- gIntersects(Sl, byid=T)
# melt matrix into edge list
intersections <- melt(intersections)
# keep only intersecting lines, remove diagonals
intersections <- subset(intersections, Var1 != Var2 & value)
# compute differences
MyDiffs = apply(intersections, 1, function(x){gDifference(Sl[x[1]], Sl[x[2]])})
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