[R] merging dataframes

[Gavin Simpson]

On Thu, 2005-11-03 at 08:33 -0500, Liaw, Andy wrote:
> The `Value' section of ?merge does say that `... in all cases the result has
> no special row names', so you're left to handle that on your own.  One
> possibility is to use
> 
>   result <- merge(mat1, mat2, all=TRUE, sort=FALSE)
> 
> so that the sorting is not done, then you can just do
> 
>   rownames(result) <- c(rownames(mat1), rownames(mat2))
> 
> Cheers,
> Andy

Thanks Roger, Andy and Dimitris for your solutions.

I'd missed the default for sort being set to TRUE - must pay more
attention in class. Roger's and Andy's approaches seem like the most
fool-proof way of canning this into a function that does all the I asked
and a bit of tidying up of NA's etc.

Cheers,

G

> 
> > From: Gavin Simpson
> > 
> > Dear List,
> > 
> > I often have to merge two or more data frames containing unique row
> > names but with some columns (names) common to the two data frames and
> > some columns not common. This toy example will explain the 
> > kind of setup
> > I am talking about:
> > 
> > mat1 <- as.data.frame(matrix(rnorm(20), nrow = 5))
> > mat2 <- as.data.frame(matrix(rnorm(20), nrow = 4))
> > rownames(mat1) <- paste("site", 1:5, sep="")
> > rownames(mat2) <- paste("site", 6:9, sep="")
> > names(mat1) <- paste("species", c(1,3,5,7), sep="")
> > names(mat2) <- paste("species", c(2,3,4,7,9), sep="")
> > mat1
> > mat2
> > 
> > So sites (rows) are unique across both data frames, but there 
> > are only 7
> > unique species (columns):
> > 
> > unique(c(names(mat1), names(mat2)))
> > 
> > merge(mat1, mat2, all = TRUE)
> > 
> > gives almost what I want, but it drops or looses the rownames()
> > information from the two merged data frames, and it re-orders the rows
> > so that one simply cannot write back the correct row names.
> > 
> > How might I go about merging two data frames as I have described, but
> > preserve the row names and more importantly, keep the order 
> > of rows the
> > same, so that rows from mat1 come before the rows of mat2?
> > 
> > Many thanks,
> > 
> > Gavin
> > -- 
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