[R] problem with using seq() or rep() inside a for loop

[William Dunlap]

   for (i in 1:(ncol(MD_dist) - 1)){
   ...
   }

Even better, replace
   1:(n-1)
with
   seq_len(n-1)
The latter does what you want (and empty integer vector) when n is 1;
the former would give c(1,0).


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Tue, Jul 7, 2015 at 2:11 PM, David Barron <dnbarron at gmail.com> wrote:

> You need to put the expression on the right of the colon in your for
> statement in parenthesis:
>
> for (i in 1:(ncol(MD_dist) - 1)){
> ...
> }
>
> On 7 July 2015 at 19:00, Karl Schilling <karl.schilling at uni-bonn.de>
> wrote:
> > Dear All:
> >
> > I want to use seq() inside a for-loop and use the looping counter i as
> the
> > "by" argument in seq(). Here is some exemplary data and code:
> >
> > # set up some data
> > distances <- c(0, NA, NA, NA, NA, NA,
> >                5, 0, NA, NA, NA, NA,
> >                5, 2, 0, NA, NA, NA,
> >                18, 5, 5, 0, NA, NA,
> >                25, 10, 8, 1, 0, NA,
> >                41, 20, 18, 5, 2, 0)
> >
> > MD_dist <- matrix(distances, ncol = 6)
> >
> > MEAN <- numeric(nrow(MD_dist) - 1) # just to set up a vector
> >
> > # loop to add (subsets of) off-diagonal diagonal values
> > for(i in 1: ncol(MD_dist) - 1){
> > diagonal <- as.vector(MD_dist[row(MD_dist) == (col(MD_dist) - i)])
> > # the following line extracts every i-th element from "diagonal"
> > diagonal.2 <- diagonal[seq(1, to = length(diagonal), by = i)]
> > MEAN[i] <- mean(diagonal.2)
> > }
> >
> > However, I keep getting the following error message:
> >
> > Error in seq.default(1, to = length(diagonal), by = i) :
> >   invalid (to - from)/by in seq(.)
> >
> > May I add that if I run the loop "by hand" - i.e. by just setting i = 1,
> > 2... etc and then running the core without the for {...} , everything
> works
> > fine.
> >
> > Further, when I use rep(..) instead of seq(...) to extract the desired
> > values from "diagonal", I have the very same problem - it works outside a
> > for loop, but fails inside.
> >
> > I am using R 3.2.1. (x64) under Win 7 Professional on a 64 bit machine.
> >
> > Any suggestion would be appreciated.
> >
> > Thank you so much.
> >
> > Karl
> >
> > --
> > Karl Schilling
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

	[[alternative HTML version deleted]]