Better moral: read the basic documentation. You missed matrix
indexing (indexing an array with a matrix subscript), and that is
described in 'An Introduction to R', section 5.3
E.g.
s$p <- match(s$prefix, colnames(y))
y[cbind(s$idx, s$p)] <- s$val
(You are trying to use different types of indices for rows (integers)
and columns (strings), and at some point strings need to be turned
into numbers.)
On Wed, 14 Jul 2010, Mario Valle wrote:
Some time ago someone asked for things that make R difficult to master. Here
I want to record one R behavior that took me off-guard yesterday. Moral of
the story: vectorialize, but don't exaggerate.
Hope it helps
mario
### A very simple data frame
tc <- textConnection(
"prefix idx val
A 1 11
A 2 22
B 1 33
B 2 44")
s <- read.table(tc, stringsAsFactors=FALSE, header=TRUE)
close(tc)
print(s)
### Matrix I want to fill with the data frame values
y <- matrix(NA, 2, 2)
colnames(y) <- c("A", "B")
### This does not work. Same values in both columns
y[s$idx, s$prefix] <- s$val
print(y)
### This works as expected
for(i in 1:4) y[s$idx[i], s$prefix[i]] <- s$val[i]
print(y)
### And also this
y[s$idx[c(1,2)], "A"] <- s$val[c(1,2)]
y[s$idx[c(3,4)], "B"] <- s$val[c(3,4)]
print(y)
--
Ing. Mario Valle
Data Analysis and Visualization Group | http://www.cscs.ch/~mvalle
Swiss National Supercomputing Centre (CSCS) | Tel: +41 (91) 610.82.60
v. Cantonale Galleria 2, 6928 Manno, Switzerland | Fax: +41 (91) 610.82.82
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--
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
______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
