[R] assign object with loop (translation from SAS to R)

[ONKELINX, Thierry]

You can use a combination of the outer() and apply() functions

n <- 10
p <- 9
dataset <- data.frame(matrix(rep(seq_len(p), each = n), nrow = n, ncol = p))
colnames(dataset) <- paste("p", seq_len(p), sep = "")
test <- t(apply(dataset, 1, function(x){ x %o% x}))
colnames(test) <- paste("p", rep(seq_len(p), each = p), "p", rep(seq_len(p), p), sep = "")
test <- test[, rep(seq_len(p), each = p) < rep(seq_len(p), p)]



ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium
+ 32 2 525 02 51
+ 32 54 43 61 85
Thierry.Onkelinx op inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey

-----Oorspronkelijk bericht-----
Van: r-help-bounces op r-project.org [mailto:r-help-bounces op r-project.org] Namens David Winsemius
Verzonden: vrijdag 29 juni 2012 16:18
Aan: lynx
CC: r-help op r-project.org
Onderwerp: Re: [R] assign object with loop (translation from SAS to R)


On Jun 28, 2012, at 9:18 PM, lynx wrote:

> I have a dataset named DM with p1, p2, ...., p9 (9 columns, numerical
> values) I would like to calculate to multify each pair of columns
> (p1p2, p1p3,...
> p1p9, p2p3, p2p4.... p8p9) and assign them in p1p2, p1p3,... p1p9,
> p2p3, p2p4.... p8p9
>
> In SAS,
>
> l=0;
> p_int_sum=0;
> do i=1 to 8;
>       do j=(i+1) to 9;
>       l=l+1;
>       p{i}p{j}=p{i}*p{j};
>       end;
> end;
>
> I would like to know how to assign them in R I tried for function but
> failed.
> for (i in 1:8) {
> for (j in 2:9) {
# Try instead:

DM[[ paste("p",i, "p",j,sep="") ]] <-
           DM[[paste("p",i, sep="")]] * DM[[paste("p",i, sep="")]]

> DM$p[i]p[j] <- DM$p[i] * DM$p[j]
>
> }}

I suspect there is a more elegant method than this use of R as a macro processor. I tested the above approach with suitably smalled subscripts on a smaller dataset:

DM <- data.frame(p1=1:10,p2=1:10,p3=1:10,p4=1:10,p5=1:10)


--
David Winsemius, MD
West Hartford, CT

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