On Thu, 8 Jan 2009, Rune Schjellerup Philosof wrote:
Browse[1]> j <- c(1,2,NA)
Browse[1]> j[j==1][-1]
[1] NA
Browse[1]> j[j==1][-2]
[1] 1
Browse[1]> j[j==1][-2] <- 2
Error during wrapup: NAs are not allowed in subscripted assignments
As far as I can see, I have no NA in the lhs (not after the second
subscript anyway).
But, it is not 'after the second subscript'. R evaluates from left to
right and does not re-evaluate subscripts in the light of subexpressions.
Think of this as (E&OE, since interpreters are far better at this than
humans)
ind <- j==1 # c(TRUE, FALSE, NA)
tmp1 <- j[ind] # c(1, NA)
tmp1[-2] <- 2 # tmp1 = c(2, 2)
j[ind] <- tmp1 # j[(c(TRUE, FALSE, NA)] <- c(2,2)
and that last is the problematic subassignment. You asked to assign the
second '2' to an unknown element of 'j': if allowed that would make all
elements NA but then the first value would be unused, so the interpreter
would think you confused.
Besides, I have a single value on the rhs, so it should be allowed to
have NAs in the lhs, according to help(Extract).
But you do not on one of your subassignments.
What am I missing?
I can see no ambiguite as to what the result of those commands should be
(j == c(2,2,NA)).
I suggest you refrain from using such complicated statements. Just
occasionally such constructs are needed for efficiency (potentially fewer
copies) but very rarely (and only by R masters).
--
Med venlig hilsen
Rune Schjellerup Philosof
Videnskabelig Assistent, Statistik, SDU
Telefon: 6550 3607
Email: rphilo...@health.sdu.dk
Adresse: J.B. Winsløwsvej 9, 5000 Odense C
--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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