[R-sig-eco] get common sampling sites from two data sets

[Christian Parker]

Etienne Laliberté wrote:
> 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)
>   
## you can also use the intersect function (does the same thing)
common_sites<-intersect(rownames(y),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,
>>>
>>> Andrés
>>>
>>> Dr. Andrés Mellado Díaz
>>>
>>> Center for Hydrological Studies CEH-CEDEX
>>> Water Quality Department
>>> Pº bajo de la Virgen del Puerto, 3
>>> 28005, Madrid
>>> SPAIN
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>>
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>>     
>
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