[R] Remove empty list from list

[Muhammad Subianto]

Dear all,
I am still working with "list".
If I have an empty list how can I remove from list data.
Here is a toy example:
x <- list(matrix(1:20, 5, 4),matrix(1:20, 5, 4),matrix(1:20, 5,
4),matrix(1:20, 5, 4),matrix(1:20, 5, 4))
y <- list(c(1, -1, -1, 1, 1),c(1, 1, -1, -1, -1),c(1, 1, 1, 1, 1),c(1,
1, -1, 1, -1),c(-1, -1, -1, -1, -1))
## Thanks to Gabor Grothendieck for this trick.
## SIMPLIFY? SIMPLIFY >< simplify
xy.list <- mapply(cbind, x, y, SIMPLIFY=FALSE)

point.class <- t(cbind(c(10,20,15,4,-1),c(21,10,15,34,-1),c(11,13,6,3,1),c(7,5,5,2,1),c(8,9,5,12,-1)))
class.diffsame <- points.neighb(as.matrix(point.class), xy.list, 5)
pd.class <- points.diff(class.diffsame,xy.list)

nc.test <- vector("list",length(pd.class))
for (i in 1:length(pd.class)) {
     nc.test[[i]] <- pd.class[[i]]$point.diff
}
nc.test
> nc.test
[[1]]
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    6   11   16    1
[2,]    4    9   14   19    1
[3,]    5   10   15   20    1

[[2]]
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    6   11   16    1
[2,]    2    7   12   17    1

[[3]]
     [,1] [,2] [,3] [,4] [,5]

[[4]]
     [,1] [,2] [,3] [,4] [,5]
[1,]    3    8   13   18   -1
[2,]    5   10   15   20   -1

[[5]]
     [,1] [,2] [,3] [,4] [,5]

>
I want to remove these:
nc.test[[3]]
nc.test[[5]]
Because my list data have more 1000 lists are there any simple way to do this?

Best, Muhammad Subianto


points.neighb <- function(p.class, list.nc, class.col) {
   ntuples <- nrow(p.class)
   instvec <- vector("list",length=ntuples)
   for (i in 1:ntuples) {
        # Thanks to Petr Pikal for this trick
        instvec[[i]]$class.diff <- (p.class[i,class.col] -
list.nc[[i]][,class.col])!=0
        instvec[[i]]$class.same <- (p.class[i,class.col] -
list.nc[[i]][,class.col])==0
   }
   instvec
}

points.diff <- function(p.class, list.nc) {
   ntuples <- length(list.nc)
   instvec <- vector("list",ntuples)
   for (i in 1:ntuples) {
        instvec[[i]]$point.diff <- list.nc[[i]][p.class[[i]]$class.diff,]
        instvec[[i]]$point.same <- list.nc[[i]][p.class[[i]]$class.same,]
   }
   instvec
}