get common sampling sites from two data sets

Here's one way.

# create matrices x and y with some sites in common
x <- matrix(1, 4, 2) ; rownames(x) <- letters[1:4]
y <- matrix(1, 4, 2) ; rownames(y) <- letters[3:6]

# identify which sites are in common for x and y
xcommon <- rownames(x) %in% rownames(y)
ycommon <- rownames(y) %in% rownames(x)
  

# create new x and y matrices with only sites shared
x2 <- x[xcommon, ]
y2 <- y[ycommon, ]


Cheers

Etienne


2011/3/17 Scott Chamberlain <scttchamberlain4 at gmail.com>

  

If your datasets are dataframes (or you could convet matrices to
dataframes), you can use

merge(x, y, by = "site")

if y sites are a subset of x that will work, but if there are some sites in
y that are not in x, then I think you would write

merge(x, y, by = "site", all = TRUE)

which will keep sites in y that are not in x, then you could just delete
sites not in x but in y

On Thursday, March 17, 2011 at 8:17 AM, Andres Mellado Diaz wrote:
    

Dear list members,

I have two data sets (sites by species) with some sites in common, one
      

with invertebrate data (X) and one with diatoms data (Y). I would like to
get both new Xc and Yc matrices showing only those sites common to X and Y,
to make similarity matrices and perform a mantel test. Hope you can help me
with this,
    

Many thanks in advance,

Andr?s

Dr. Andr?s Mellado D?az

Center for Hydrological Studies CEH-CEDEX
Water Quality Department
P? bajo de la Virgen del Puerto, 3
28005, Madrid
SPAIN
 [[alternative HTML version deleted]]

       [[alternative HTML version deleted]]

	[[alternative HTML version deleted]]

  
------------------------------------------------------------------------