[R] Selecting elements from all items in a list

[Dimitris Rizopoulos]

How about:

l <- list("")
l[[1]] <- c("A1","A2","A3")
l[[2]] <- c("B1","B2","B3")
l[[3]] <- c("C1","B2","B3")


lapply(l, "[[", 2)

or

sapply(l, "[[", 2)


I hope it helps.

Best,
Dimitris


On 2/14/2012 2:44 PM, geotheory wrote:
> Basic question (if you know the answer)...  I am dealing with a list of
> commonly-formatted sub-lists, for example:
>
> l<- list("")
> l[[1]]<- c("A1","A2","A3")
> l[[2]]<- c("B1","B2","B3")
> l[[3]]<- c("C1","B2","B3")
>
> Lets say I need to extract every 2nd item (i.e. A2, B2, C2).  [[]] cannot be
> used.   l[2] returns practically the same as l[[2]].  Is there a way to
> achieve this without having to loop or convert to data.frame?
>
> Thanks in advance.
>
> --
> View this message in context: http://r.789695.n4.nabble.com/Selecting-elements-from-all-items-in-a-list-tp4387045p4387045.html
> Sent from the R help mailing list archive at Nabble.com.
>
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-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
Web: http://www.erasmusmc.nl/biostatistiek/