[R] matching rows in matrices

[Gabor Grothendieck]

If A and B are first and second matrix respectively then try:

rowSums(inner(A, t(B), identical))

where the generalized inner product, inner, is defined in this post:

http://tolstoy.newcastle.edu.au/R/e4/help/08/08/19562.html

On Thu, Jul 2, 2009 at 8:27 AM, dreamworx<Andy_woolston at hotmail.com> wrote:
>
> I have a matrix such as this,
>
>     [,1] [,2] [,3]
> [1,]    1    1    2
> [2,]    2    5    5
>
> and a larger matrix such as this,
>
>     a  b
> [1,] 1  5
> [2,] 2  5
> [3,] 4  9
> [4,] 5  8
> [5,] 7  8
> [6,] 7 10
> [7,] 9 10
>
> what I want to do is check the number of times the columns in the first
> matrix appear as rows in the second matrix. So for instance in this example
> 1,5  and 2,5 appear in both so I'd want R to return the number 2. Is there a
> function to do this?
> --
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>
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