# Re: [R] Remove empty list from list

Date: Tue 29 Aug 2006 - 03:43:50 EST

On this day 28/08/2006 19:20, Muhammad Subianto wrote:
> 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?
>
>
>
> 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
> }
>

Dear
Jim Holtman and Gabor Grothendieck,
Thank you both very much for the suggestions! These is exactly what I was looking for.

## delete null/empty entries in a list
delete.NULLs <- function(x.list){

x.list[unlist(lapply(x.list, length) != 0)] }

> delete.NULLs <- function(x.list){
+ x.list[unlist(lapply(x.list, length) != 0)] + }
> delete.NULLs <- function(x.list){
+ x.list[unlist(lapply(x.list, length) != 0)] + }
>
> delete.NULLs(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]
[1,] 3 8 13 18 -1
[2,] 5 10 15 20 -1

>

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue Aug 29 04:10:34 2006

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