Re: [R] Vector comparison to matrix

From: Ravi Varadhan <>
Date: Mon 15 Aug 2005 - 23:49:09 EST

Hi Todd,

Here is a function that was suggested to me by Gabor Grothendieck. This function counts the number of times each row of a matrix B occurs in another matrix A.

rowmatch.count <- function(a,b) {

    f <- function(...) paste(..., sep=":")
    a2 <-"f",
    b2 <-"f",
    c(table(c(a2,unique(b2)))[b2] - 1)

If you are interested in finding the number of occurrences of a vector "b" instead, you can call this function as follows:


Hope this is helps,

> -----Original Message-----
> From: [mailto:r-help-
>] On Behalf Of Todd Remund
> Sent: Monday, August 15, 2005 1:13 AM
> To:
> Subject: [R] Vector comparison to matrix
> I am looking for a fast way to count the number of rows in a matrix are
> identical to a pattern vector. For example, if I am interested in
> counting
> the number of row vectors in a matrix that are identical to (1,2,3) what
> would I do? I have tried the identical statement in a loop but this is
> far
> too slow. I have a very large matrix and need to avoid loops at all
> costs.
> Thanks for any help.
> Todd Remund
> ______________________________________________
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> PLEASE do read the posting guide!
> guide.html mailing list PLEASE do read the posting guide! Received on Mon Aug 15 23:55:02 2005

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