Accessing selected elements of a list

Thanks! I think one quick solution (from another answer that just arrived) is:

jlist[ sapply(jlist,length) > 0 ]

G.


On Nov 8, 2012, at 10:57 AM, arun wrote:

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: Gon?alo 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!
>
>______________________________________________
>R-help at r-project.org mailing list
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>PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.
>
>

Gon?alo Ferraz, PhD
Biological Dynamics of Forest Fragments Project
Smithsonian Tropical Research Institute / Instituto Nacional de Pesquisas da Amaz?nia

http://ferrazlab.com/LabSite/Welcome.html

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