On Mar 30, 2010, at 11:47 AM, Dgnn wrote:
I have what may be a simple/foolish question, but I've done the due
diligence
and looked through pages of posts here as well as several of the
PDFs on the
CRAN site, but haven't been able find what I'm after.
I am working with a list of say 3 histogram objects A, B & C, and each
histogram is a list of 7 elements. I would like to access $name, the
6th
element, of histograms A,B and C.
If you want better answers, you should provide better examples ...
with _CODE_.
Trial and error yielded some results that told me I clearly don't
understand
how R interprets index commands. For the histogram list above:
a[1:2] give histograms A and B as expected.
a[[1:2]] gives the second element of histogram 1, but a[[1:1]] gives
all
elements of histogram 1, while a[[1:3]] gives null?!
If anyone could help with an explanation of indexing rules, or a
source that
does so, I would very much appreciate it. Oh and an answer to the
first
question!
?"[["
"[[" always returns a single vector or list and so its arguments will
be coerced to a single value. When passed an arguemnt that has
multiple values it is interpreted as serial application of "[[" with
the serial values. The construction [[1:1]] gets turned into [[1]]
(since 1:1 is just 1) while the construction [[1:2]] got turned into
[[1]][[2]]
> list(a=list(aa=5, bb=6),b=2,c=3)[[1:2]]
[1] 6
"[" may return a more complex object and so may accept multiple
arguments
> list(a=1,b=2,c=3)[c(1,3)]
$a
[1] 1
$c
[1] 3
--
David Winsemius, MD
West Hartford, CT
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