[R] Problem in cluster sampling: 'mixed with negative subscripts'

[Bert Gunter]

Inline...


On Sat, Dec 19, 2020 at 9:22 PM Richard O'Keefe <raoknz using gmail.com> wrote:

> More accurately, in x[i] where x and i are simple vectors,
> i may be a mix of positive integers and zeros
>   where the zeros contribute nothing to the result
> or it may be a MIX of negative integers and zeros
>   where the zeros contribute nothing to the result
>   and -k means "do not include element k".
> It would be nice to write things like
>   x[c(-1,1)]
> meaning to copy everything except element 1, then
> element 1.  But that is not allowed.
>

But c(x[-1], x[1])  is, which is not so terrible, after all...

Cheers,
Bert


>
> On Sun, 20 Dec 2020 at 10:20, Jim Lemon <drjimlemon using gmail.com> wrote:
>
> > Hi Chao,
> > You have discovered one of the surprising things about the extraction
> > operator "[". It expects to get an object consisting of integers (like
> > 1,2,3,...) or logical values (TRUE,FALSE or 0,1). As you have passed
> > the _values_ of your cluster, it can't deal with the negative numbers
> > as they don't index anything in the original object. If you get rid of
> > the negative values by applying the abs() function, it will seem to
> > work, but you aren't getting what you expected or anything sensible.
> > Here's an example:
> >
> > # get a vector of positive and negative real numbers
> > x1<-rnorm(10)
> > x1
> > [1] -0.2174320 -1.3185389  0.4049751  0.4780766 -1.6317983  3.4265246
> > [7]  2.0721620  1.1590961  0.9896266  0.5672552
> > # try to index it with its values
> > x[x]
> > # Error in x[x] : only 0's may be mixed with negative subscripts
> > # now change the negative values to positive ones
> >  x1[abs(x1)]
> > # No error, but you only get some of the values!
> > [1] -0.2174320 -0.2174320  0.4049751 -1.3185389 -0.2174320
> > abs(x1)
> > [1] 0.2174320 1.3185389 0.4049751 0.4780766 1.6317983 3.4265246 2.0721620
> > [8] 1.1590961 0.9896266 0.5672552
> > # What the extraction operator does is attempt to get valid {positive}
> > integer indices
> > # or zeros. Then it can use the positive values and discard the zeros
> > as.integer(abs(x1))
> > [1] 0 1 0 0 1 3 2 1 0 0
> >
> > Now the error message makes a lot more sense.
> >
> > Jim
> >
> > On Sun, Dec 20, 2020 at 5:58 AM Chao Liu <psychaoliu using gmail.com> wrote:
> > >
> > > Hi,
> > >
> > > I was trying to do a cluster sampling but came across this error: Error
> > in
> > > xj[i] : only 0's may be mixed with negative subscripts. What is the
> cause
> > > and how to get around? Thank you for your help!
> > >
> > > Here is the code:
> > >
> > > #simulate some data
> > > y <- rnorm(20)
> > > x <- rnorm(20)
> > > z <- rep(1:5, 4)
> > > w <- rep(1:4, each=5)
> > > dd <- data.frame(id=z, cluster=w, x=x, y=y)
> > > clusters <- split(dd, dd$cluster) #split into clusters
> > > k <- length(clusters) #length of clusters
> > > # This function generates a cluster sample
> > > clsamp <- function() dd[unlist(clusters[sample.int(k, k, replace =
> > TRUE)],
> > > use.names = TRUE), ]
> > > clsamp()
> > >
> > >
> > > I got this error: Error in xj[i] : only 0's may be mixed with negative
> > > subscripts.
> > >
> > >
> > > Best,
> > >
> > > Chao
> > >
> > >         [[alternative HTML version deleted]]
> > >
> > > ______________________________________________
> > > R-help using 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 using 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]]
>
> ______________________________________________
> R-help using 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]]