[R] Intersection of 2 matrices

[Michael Kao]

On 2/12/2011 2:48 p.m., David Winsemius wrote:
>
> On Dec 2, 2011, at 4:20 AM, oluwole oyebamiji wrote:
>
>> Hi all,
>>     I have matrix A of 67420 by 2 and another matrix B of 59199 by 2. 
>> I would like to find the number of rows of matrix B that I can find 
>> in matrix A (rows that are common to both matrices with or without 
>> sorting).
>>
>> I have tried the "intersection" and "is.element" functions in R but 
>> it only working for the vectors and not matrix
>> i.e,    intersection(A,B) and is.element(A,B).
>
> Have you considered the 'duplicated' function?
>

Here is an example based on the duplicated function

test.mat1 <- matrix(1:20, nc = 5)

test.mat2 <- rbind(test.mat1[sample(1:5, 2), ], matrix(101:120, nc = 5))

compMat <- function(mat1, mat2){
     nr1 <- nrow(mat1)
     nr2 <- nrow(mat2)
     mat2[duplicated(rbind(mat1, mat2))[(nr1 + 1):(nr1 + nr2)], ]
}

compMat(test.mat1, test.mat2)