R help - Dec 2020 - Problem in cluster sampling: 'mixed with negative subscripts'

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 at 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 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.

Jim and Bert,

Thank you for your help. It was an indexing problem. I was able to solve it
by changing the split line to: clusters <- split(seq_len(nrow(dd)),
dd$cluster).
Thank you.

Best,

Chao


On Sat, Dec 19, 2020 at 4:19 PM Jim Lemon <drjimlemon at 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 at 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 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]]

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.


On Sun, 20 Dec 2020 at 10:20, Jim Lemon <drjimlemon at 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 at 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 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]]