[R] Accessing selected elements of a list

[arun]

Hi,
If i understand it correctly,

lapply(jlist,function(x) x[x>0])
#[[1]]
#NULL

#[[2]]
#[1] 1

#[[3]]
#NULL

#[[4]]
#[1] 1 2 3

#[[5]]
#NULL
A.K.



----- Original Message -----
From: Gonçalo Ferraz <gferraz29 at gmail.com>
To: r-help at r-project.org
Cc: 
Sent: Thursday, November 8, 2012 9:42 AM
Subject: [R] Accessing selected elements of a list

Hi,


If I have a vector:

junk <- c(2,0,0,3,0)

and want to access, say, all the elements that are greater than zero. I just do:

junk[which(junk>0)]



Now, If I have a list:

jlist <- list(NULL,c(1,0),NULL,c(1,2,3), NULL)

and want to access all the elements that have length greater than zero, I know how to find the elements with:

which(sapply(jlist,length)>0)

But how do I get a new list, only with the non-zero-length elements, without having to write a for loop?

I tried:

notnull <- which(sapply(jlist,length)>0)
jlist[[notnull]]

and got the error:

Error in jlist[[notnull]] : recursive indexing failed at level 2

Thank you for any help!

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