Thanks Rui and Arun.
Both worked well.

One more question, what shall I add for Rui's code if only the comparison
of TRUE (no FALSE) to be shown in the result?

Elaine

code
different <- function(x, y) x == 1 & y == 0

set.seed(7054)
mat <- matrix(sample(0:1, 500, TRUE), nrow = 5)
rownames(mat) <- LETTERS[1:5]
colnames(mat) <- sprintf("D%03d", 1:100)

different(mat["B",], mat["E",])


On Fri, Sep 27, 2013 at 9:31 PM, arun <smartpink111@yahoo.com> wrote:

> Just to add:
>
> If you wanted the difference of every combination of rows:
> set.seed(248)
>  mat1<-
> matrix(sample(0:1,5*100,replace=TRUE),ncol=100,dimnames=list(LETTERS[1:5],paste0("D",sprintf("%03d",1:100)))
> )
>  dat<-expand.grid(LETTERS[1:5],LETTERS[1:5],stringsAsFactors=FALSE)
> dat1<-dat[!paste0(dat[,1],dat[,2]) %in% paste0(LETTERS[1:5],LETTERS[1:5]),]
>  lst1<- lapply(seq_len(nrow(dat1)),function(i)
> {x<-mat1[unlist(dat1[i,]),]; which(different(x[1,],x[2,]))}) #using Rui's
> function
> names(lst1)<- paste(dat1[,1],dat1[,2],sep="_")
>
>
> A.K.
>
>
>
> ----- Original Message -----
> From: Rui Barradas <ruipbarradas@sapo.pt>
> To: Elaine Kuo <elaine.kuo.tw@gmail.com>
> Cc: "r-help@r-project.org" <r-help@r-project.org>
> Sent: Friday, September 27, 2013 7:39 AM
> Subject: Re: [R] Compare species presence and absence between sites
>
> Hello,
>
> Something like this?
>
>
> different <- function(x, y) x == 1 & y == 0
>
> set.seed(7054)
> mat <- matrix(sample(0:1, 500, TRUE), nrow = 5)
> rownames(mat) <- LETTERS[1:5]
> colnames(mat) <- sprintf("D%03d", 1:100)
>
> different(mat["B",], mat["E",])
>
>
>
> Hope this helps,
>
> Rui Barradas
>
> Em 27-09-2013 11:48, Elaine Kuo escreveu:
> > Dear List,
> >
> >
> >
> > I want to compare the presence and absence of bird species based on the
> > sites in a matrix.
> >
> > The matrix has 5 rows for Island A, B, C, D, and E.
> >
> > It has 100 columns for bird species D001-D100.
> >
> > In each cell of the matrix,
> >
> > the presence-absence of bird species will be recorded as 1 or 0.
> >
> > (For example, if species D001 is found on Island D,
> >
> > the matrix cell of species D001 and Island D will be 1.)
> >
> >
> >
> > Now I want to know the different bird species between Island B and E.
> >
> > In other words, I would like to find out bird species present (1) on
> Island
> > B but absent (0)on island E, and vice versa (absent (0) on Island B but
> > present (1)on island E).
> >
> >
> >
> > Please kindly advise how to code the purpose above.
> >
> > Thank you in advance.
> >
> >
> >
> > Elaine
> >
> >     [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > 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@r-project.org mailing list
> 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]]

