[R] Automatic routine - NEW

Spencer Graves spencer.graves at pdf.com
Wed Jun 23 15:46:14 CEST 2004

  The documentation is good for things like this. In most (all recent?) 
versions of R, "help.start()" brings up a help page. Select "An 
Introduction to R", and go to "Vector Indices". Also look at "Arrays and 
Matrices: Array Indexing". There, you will find that "DF[3:5,]" might be 
what you want.

Actually, I'm not certain that your "c" below is what you want, because 
class(c[1,1]) is "list", and I could not do arithmetic on it. I 
discovered that when I tried all.equal(c, DF[3:5,]). {Also, "c" is the 
name of a very useful function; try "?c". It is usually wise to avoid 
using names of functions for matrices of data.frames. R will select the 
one you want from the context in most but not all cases.}

hope this helps.
spencer graves

Monica Palaseanu-Lovejoy wrote:

>Hi Again,
>First of all thank you for all the responses to my previous query. 
>Your answers were very helpful and I did the job ;-). Now I hope you 
>can answer as quick the following (sorry I am invading you with 
>trivial questions):
>Let’s use again the following data.frame example:
>DF <- data.frame(x=rnorm(5), y=rnorm(5))
>I want to obtain a new data.frame (or matrix) that contains only n 
>rows (from the i rows DF has), and all the columns. If I have to do it 
>step by step I would do something like that, for example:
>a3 <- DF[3,]
>a4 <- DF[4,]
>a5 <- DF[5,]
>b <- data.frame(a3, a4, a5)
>c <- matrix(b, nrow=3, ncol=2, byrow=TRUE)
>Now I want to do the same in one go, so I wrote:
>for (i in 3:5)
>	d[i] <- DF[i,]
>	e <- data.frame(d[i])
>	f <- matrix(e, ncol=2, nrow=3, byrow=TRUE)
>Which of course gives me errors and the matrix f has all elements 
>equal with DF[5,5]. If I don’t use [i] after d, the resulting f matrix is 
>made up from the DF[5,] elements (which is quite normal since i 
>replaces itself ...). So ..... How is this done correctly?
>I am really appreciating your time and effort to answer me,
>R-help at stat.math.ethz.ch mailing list
>PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html

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