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How to drop null elements of a list?

To: s-news@wubios.wustl.edu
Subject: How to drop null elements of a list?
From: "Patrick Joseph" <patrick_nospam@hotmail.com>
Date: Mon, 23 Aug 2004 10:19:33 -0400

Hi,

I have a list named lst which has an arbitrary number of named elements. For example:

print(lst)
$a:
[1] 10

$b:
[1] 20

I would like to extract the elements that match a vector of names but I want the result contains only the matched elements. For example, if I do the following command:

lst.match _ lst[c("a","c")]

I would like the result:
$a:
[1] 10

and not:
$a:
[1] 10


$"":
NULL


Is there a simple way to do that (maybe something that uses drop) other than doing a second command like:

lst.match[unlist(lapply(lst.match,function(x) !is.null(x)))]

Thank you for any hint,
Patrick

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