1
我需要爲每個嵌套循環中的每個i計算一個總和,如下所示,然後將每個i的總和作爲列表輸出。問題是代碼對於大量的觀察來說非常慢。有什麼辦法可以避免循環,以便代碼運行速度更快?謝謝。在R中計算嵌套循環不平衡縱向數據
#### generate data
set.seed(234)
N=3
v<-sample(2:6,N,replace=TRUE)
id<-c(rep(1:N,v))
n<-length(id)
x<-as.matrix(cbind(rnorm(n,0,1),rnorm(n,0,1),rnorm(n,0,1)))
x1<-cbind(id,x)
e<-runif(3)
> v
[1] 5 5 2
id
[1] 1 1 1 1 1 2 2 2 2 2 3 3
> x
[,1] [,2] [,3]
[1,] 0.7590390 -0.8716028 -0.30554099
[2,] 0.3713058 1.1876234 0.86956546
[3,] 0.5758514 -0.6672287 -1.06121591
[4,] -0.5703207 0.5383396 -0.09635967
[5,] 0.1198567 0.4905632 0.47460932
[6,] 0.2095484 -1.0216529 -0.02671707
[7,] -0.1481357 -0.3726091 1.10167492
[8,] 0.6433900 1.3251178 -0.26842418
[9,] 1.1348350 -0.7313432 0.01035965
[10,] 0.1995994 0.7625386 0.25897152
[11,] 0.2987197 0.3275333 -0.39459737
[12,] -0.3191671 -1.1440187 -0.48873668
> e
[1] 0.3800745 0.5497359 0.3893235
### compute sum
sumterm_<-list()
count=1
for (i in 1:N){
idd=x1[,1]==i
xi=x[idd,]
sumterm=matrix(rep(0,N*N),nrow=3,ncol=3)
for (j in 1:v[i]){
xij=xi[j,]
sumterm=sumterm+as.matrix(xij-e)%*%(xij-e)
count=count+1
}
sumterm_[[i]]<-sumterm
}
sumterm_
[[1]]
[,1] [,2] [,3]
[1,] 1.1529838 -0.7562553 -0.1121242
[2,] -0.7562553 3.9117383 3.0597216
[3,] -0.1121242 3.0597216 3.0606953
[[2]]
[,1] [,2] [,3]
[1,] 0.97965490 -0.04598867 -0.74102232
[2,] -0.04598867 5.60764839 -0.05553464
[3,] -0.74102232 -0.05553464 1.27377151
[[3]]
[,1] [,2] [,3]
[1,] 0.4955573 1.202421 0.6777518
[2,] 1.2024208 2.918179 1.6614076
[3,] 0.6777518 1.661408 1.3855215
你正在成長你的對象。 R中的菜鳥101錯誤預先分配所有內容並填寫結果。 。請參閱[R Inferno](http://www.burns-stat.com/documents/books/the-r-inferno/)獲取有關如何避免不當行爲的更多提示。 –