在data.table中应用按行返回列表/矩阵的函数 [英] Applying a function returning list/matrix row-wise in data.table
问题描述
I am trying to do the steps mentioned in http://flowingdata.com/2011/05/11/how-to-map-connections-with-great-circles/ but using data.table. Especially step 8 listed there. Attached are my steps and the problem I'm running into:
library(data.table)
library(maps)
library(geosphere)
airports <- as.data.table(read.csv("http://datasets.flowingdata.com/tuts/maparcs/airports.csv", header=TRUE))
flights <- as.data.table(read.csv("http://datasets.flowingdata.com/tuts/maparcs/flights.csv", header=TRUE, as.is=TRUE))
setnames(airports,c("airport1",names(airports)[2:7]))
setkey(flights,airport1)
setkey(airports,airport1)
ap <- merge(flights,airports)
setkey(ap,airport2)
setnames(airports,c("airport2",names(airports)[2:7]))
setkey(airports,airport2)
setkey(ap,airport2)
ap2 <- merge(ap,airports)
ap3 <- ap2[,.(airport1,airport2,airline,cnt,lat.x,long.x,lat.y,long.y)]
## ap3[,inter:=gcIntermediate(c(long.x,lat.x),c(long.y,lat.y),n=100,addStartEnd=TRUE),] ## Error in .pointsToMatrix(p1) : Wrong length for a vector, should be 2
## ap3[,inter:=gcIntermediate(c(long.x,lat.x),c(long.y,lat.y),n=100,addStartEnd=TRUE),] ## Error in .pointsToMatrix(p1) : Wrong length for a vector, should be 2
##
## Tried some more stuff but no luck!
## fn <- function(lonx,latx,lony,laty) gcIntermediate(c(lonx,latx),c(lony,laty),n=100,addStartEnd=TRUE)
## ap3[,do.call(fn,.SD),.SDcols=5:8] ## Error in (function (lonx, latx, lony, laty) : unused arguments (lat.x = c(35.21401111, 35.2140 ... snip ...
因此，我搜索了stackoverflow，并尝试了[1]和[2]中列出的步骤，但是无法正常工作.我记得读过某个地方(虽然现在找不到)，但data.table可以存储列表，但我不知道该怎么做.另外，除了FAQ 2.9节中列出的内容之外，还有什么方法可以调试 j 中的函数?
So I searched stackoverflow and tried steps listed in [1] and [2] but couldn't get it to work. I remember reading somewhere (cannot find it now though) that data.table can store lists but I cannot figure out how. Also, is there some way to debug functions in the j apart from what's listed in the Section 2.9 of the FAQ?
推荐答案
这实际上应该是注释，但不适合该注释:对于分别由c(long.x，lat.x)和c(long.y，lat.y)定义的每个p1和p2，您都有一个矩阵(或列表)(此后，我仅关注矩阵)和该矩阵的维数取决于n和addStartEnd的值.例如，如果设置n = 1且addStartEnd = FALSE，则将返回尺寸为1乘2的矩阵；如果设置n = 1且addStartEnd = TRUE，则将返回尺寸为3乘2的矩阵.现在，使用像您一样的data.table操作，您不能简单地附加值.我不是data.table专家，但是我认为正确的方法是，您必须先进行行操作，然后使用 rbindlist .例如，
This should be really a comment, but it doesn't fit there:
For each p1 and p2 as defined by c(long.x,lat.x) and c(long.y,lat.y), respectively, you have a matrix (or a list) (hereafter, I focus on the matrix only) and dimension of that matrix depends on values of n and addStartEnd. For example, if you set n=1 and addStartEnd=FALSE, it will return a matrix of dimension of 1 by 2, and if you set n=1 and addStartEnd=TRUE, it will return a matrix of dimension of 3 by 2. Now, with data.table operation like yours, you can't simply append the values. I am not a data.table expert, but what I think a right way, is that you have to do rowwise operation and then use rbindlist.,e.g.,
apt<-setDT(ap3)
tt<-rbindlist(lapply(1:nrow(apt),function(i)cbind(apt[i,],gcIntermediate(apt[i,c("long.x","lat.x")],apt[i,c("long.y","lat.y")],n=100,addStartEnd=TRUE))))
> tt
airport1 airport2 airline cnt lat.x long.x lat.y long.y lon lat
1: CLT ABE all 56 35.21401 -80.94313 40.65236 -75.4404 -80.94313 35.21401
2: CLT ABE all 56 35.21401 -80.94313 40.65236 -75.4404 -80.89245 35.26904
3: CLT ABE all 56 35.21401 -80.94313 40.65236 -75.4404 -80.84171 35.32405
4: CLT ABE all 56 35.21401 -80.94313 40.65236 -75.4404 -80.79090 35.37904
5: CLT ABE all 56 35.21401 -80.94313 40.65236 -75.4404 -80.74002 35.43401
---
510710: PHX YUM YV 328 33.43417 -112.00806 32.65658 -114.6060 -114.50396 32.68840
510711: PHX YUM YV 328 33.43417 -112.00806 32.65658 -114.6060 -114.52947 32.68045
510712: PHX YUM YV 328 33.43417 -112.00806 32.65658 -114.6060 -114.55498 32.67250
510713: PHX YUM YV 328 33.43417 -112.00806 32.65658 -114.6060 -114.58048 32.66454
510714: PHX YUM YV 328 33.43417 -112.00806 32.65658 -114.6060 -114.60597 32.65658
按照@Frank的建议:您可以仅使用data.table操作(其中102 = 100(n)+ 2(addStartEnd = TRUE))进行以下操作
As per the suggestion of @Frank: you can proceed as follows using only data.table operation (where 102 =100 (n)+ 2 (addStartEnd=TRUE))
ap3[,gcIntermediate(c(long.x,lat.x),c(long.y,lat.y),n=100,addStartEnd=TRUE),by=1:nrow(ap3)][,list(lon=head(V1,102),lat=tail(V1,102)),by=nrow]
nrow lon lat
1: 1 -80.94313 35.21401
2: 1 -80.89245 35.26904
3: 1 -80.84171 35.32405
4: 1 -80.79090 35.37904
5: 1 -80.74002 35.43401
---
510710: 5007 -114.50396 32.68840
510711: 5007 -114.52947 32.68045
510712: 5007 -114.55498 32.67250
510713: 5007 -114.58048 32.66454
510714: 5007 -114.60597 32.65658
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