[R] extracting components of a list

From: Robin Hankin <r.hankin_at_noc.soton.ac.uk>
Date: Tue 14 Jun 2005 - 00:23:21 EST


how do I extract those components of a list that satisfy a certain requirement? If

jj <- list(list(a=1,b=4:7),list(a=5,b=3:6),list(a=10,b=4:5))

I want just the components of jj that have b[1] ==4 which in this case would be the first and
third of jj, viz list (jj[[1]],jj[[3]]).

How to do this efficiently?

My only idea was to loop through jj, and set unwanted components to NULL, but
FAQ 7.1 warns against this.

Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743

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Received on Tue Jun 14 00:27:50 2005

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