[R] Write columns from within a list to a matrix?

[Benilton Carvalho]

test <- lapply(1:3, function(i) cbind(runif(15), rnorm(15,2)))
sapply(test, "[", 16:30)

b

On Jul 22, 2007, at 3:39 PM, jrg66 at comcast.net wrote:

> Hello,
>
> I think I have a mental block when it comes to working with lists.   
> lapply and sapply appear to do some magical things, but I can't  
> seem to master their usage.
>
> As an example, I would like to convert a column within a list to a  
> matrix, with the list element corresponding to the new matrix column.
>
> #Here is a simplified example: .
> test=vector("list", 3)
> for (i in 1:3){ test[[i]]=cbind(runif(15), rnorm(15,2)) }  #create  
> example list (I'm sure there is a better way to do this too).
>
> #Now, I wan to get the second column back out, converting it from a  
> list to a matrix.  This works, but gets confusing/inefficient when  
> I have multiple complex lists I am trying to manage.
>
> savecol2=matrix(0,15,0)
> for (i in 1:3){
> savecol2=cbind(savecol2, test[[i]][,1])
> }
>
> #Something like??:  (of course this doesn't work)
> savecol2=sapply(test, "[[", function(x) x[2,])
>
> Thank you!
>
> Jeff
>
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