OK...I'll put in my 2 cents worth. 

It seems to me that the problem is with this line:

b$a=a , where "s" is something other than a vector with
length equal to nrow(b).

I had no idea that a dataframe could hold a dataframe. It is not just
rbind(b,b) that fails, apply(b,1,sum) fails and so does plot(b). I'll 
bet other R commands fail as well.

My point of view is that a dataframe is a list of vectors
of equal length and various types (this is not exactly what the help
page says, but it is what it suggests to me). 

Hum, I wonder how much code is based on the idea that a dataframe can hold 
a
dataframe. 15 years of using R just isn't enough! But, I can say that not 
one
line of code I've written expects a dataframe to hold a dataframe.

> Hi,

> The following was already a topic on r-help, but after understanding 
what is
> going on, I think it fits better in r-devel.

> The problem is this:
> When a data.frame has another data.frame in it, rbind doesn't work well.
> Here is an example:
> --
> > a=data.frame(x=1:10,y=1:10)
> > b=data.frame(z=1:10)
> > b$a=a
> > b
> z a.x a.y
> 1   1   1   1
> 2   2   2   2
> 3   3   3   3
> 4   4   4   4
> 5   5   5   5
> 6   6   6   6
> 7   7   7   7
> 8   8   8   8
> 9   9   9   9
> 10 10  10  10
> > rbind(b,b)
> Error in `row.names<-.data.frame`(`*tmp*`, value = c("1", "2", "3", "4", 
 :
> duplicate 'row.names' are not allowed
> In addition: Warning message:
> non-unique values when setting 'row.names': ?1?, ?10?, ?2?, ?3?, ?4?, 
?5?,
> ?6?, ?7?, ?8?, ?9?
> --

> 
> Looking at the code of rbind.data.frame, the error comes from the
> lines:
> --
> xij <- xi[[j]]
> if (has.dim[jj]) {
> value[[jj]][ri, ] <- xij
> rownames(value[[jj]])[ri] <- rownames(xij)   # <--  problem is here
> }
> --
> if the rownames() line is dropped, all works well. What this line
> tries to do is to join the rownames of internal elements of the
> data.frames I try to rbind. So the result, in my case should have a
> column 'a', whose rownames are the rownames of the original column 'a'. 
It
> isn't totally clear to me why this is needed. When would a data.frame
> have different rownames on the inside vs. the outside?

> Notice also that rbind takes into account whether the rownames of the
> data.frames to be joined are simply 1:n, or they are something else.
> If they are 1:n, then the result will have rownames 1:(n+m). If not,
> then the rownames might be kept.

> I think, more consistent would be to replace the lines above with
> something like:
> if (has.dim[jj]) {
> value[[jj]][ri, ] <- xij
> rnj = rownames(value[[jj]])
> rnj[ri] = rownames(xij)
> rnj = make.unique(as.character(unlist(rnj)), sep = "")
> rownames(value[[jj]]) <- rnj
> }

> In this case, the rownames of inside elements will also be joined, but
> in case they overlap, they will be made unique - just as they are for
> the overall result of rbind. A side effect here would be that the
> rownames of matrices will also be made unique, which till now didn't
> happen, and which also doesn't happen when one rbinds matrices that
> have rownames. So it would be better to test above if we are dealing
> with a matrix or a data.frame.

> But most people don't have different rownames inside and outside.
> Maybe it would be best to add a flag as to whether you care or don't
> care about the rownames of internal data.frames...

> But maybe data.frames aren't meant to contain other data.frames?

> If instead I do
> b=data.frame( z=1:10, a=a)
> then rbind(b,b) works well. In this case the data.frame was converted to 
its
> columns. Maybe
> b$a = a
> should do the same?

> Michael
> --
> View this message in context: http://r.789695.n4.nabble.com/rbind-
> on-data-frame-that-contains-a-column-that-is-also-a-data-frame-
> tp2315682p2315682.html
> Sent from the R devel mailing list archive at Nabble.com.

> ______________________________________________
> R-devel@r-project.org mailing list
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