[R] list indexing

[David Orme]

Hello

I've got a question about  list indexing. If anyone can help or point 
in the direction of some documentation, that'd be great. I've checked 
the Introduction to R and R language definition.

Say you have a list of vectors:

>  x_list(c("a","b","c"),c("a","b","c","d"),c("a","b"),c("a","b","c","d","e"))
>  x
[[1]]
[1] "a" "b" "c"

[[2]]
[1] "a" "b" "c" "d"

[[3]]
[1] "a" "b"

[[4]]
[1] "a" "b" "c" "d" "e"

Indexing single list components is fine using [[i]] and elements 
within using [[i]][j] but what if you want to get some information, 
for instance vector length or attributes of the components, across 
(or should that be down) the top level components. You can do it by 
looping across 1:length(list):

>  store <- numeric(0)
>  for(components in 1:length(x)) store <- c(store,length(x[[components]]))
>  store
[1] 3 4 2 5

I know it's only two lines of code. I  guess I'm wondering whether 
there is something that does what I'd expect from length(x[[1:4]]) if 
[[i]] allowed multiple indices.

Thanks,
David Orme.

-- 

---------------------------------
David Orme
Ph.D. Student - Macroevolution and diversity.

Department of Biology,
Imperial College,
Silwood Park,
Ascot,
Berkshire.
UK.
SL5 7PY

Phone:	(020) 759 42446	(wk.)
	(01344) 891539	(hm.)

E-mail:	d.orme at ic.ac.uk
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