Jim I tried that and it works. Thank you very much for your help!
Regards Pietro -----Original Message----- From: jim holtman [mailto:jholt...@gmail.com] Sent: 04 November 2011 13:38 To: Parodi, Pietro Cc: r-help@r-project.org Subject: Re: [R] Counting number of common elements between the rows of two different matrices Try this: # create dummy data a <- matrix(sample(20, 50, TRUE), ncol = 5) b <- matrix(sample(20, 50, TRUE), ncol = 5) # create combinations to test x <- expand.grid(seq(nrow(a)), seq(nrow(b))) # test result <- mapply(function(m1, m2) any(a[m1, ] %in% b[m2, ]) , x[, 1] , x[, 2] ) # create the output matrix result.m <- matrix(result, nrow = nrow(a), ncol = nrow(b)) On Fri, Nov 4, 2011 at 8:51 AM, Parodi, Pietro <pietro.par...@willis.com> wrote: > > Hello > > I'm trying to solve this problem without using a for loop but I have so > far failed to find a solution. > > I have two matrices of K columns each, e.g. (K=5), and with numbers of > row N_A and N_B respectively > > A = (1 5 3 8 15; > 2 7 20 11 13; > 12 19 20 21 43) > > B = (2 6 30 8 16; > 3 8 19 11 13) > > (the actual matrices have hundreds of thousands of entry, that's why I'm > keen to avoid "for" loops) > > And what I need to do is to apply a function which counts the number of > common elements between ANY row of A and ANY row of B, giving a result > like this: > > > A1 vs B1: 1 # (8 is a common element) > A1 vs B2: 1 # (8 is a common element) > A2 vs B1: 1 # (2 is a common element) > A2 vs B2: 1 # 11, 13 are common elements > Etc. > > I've built a function that counts the number of common elements between > two vectors, based on the intersect function in the R manual > > common_elements <- function(x,y) length(y[match(x,y,nomatch=0)]) > > And a double loop who solves my problem would be something like > (pseudo-code) > > For(i in 1:N_A){ > for(j in 1:N_B){ > ce(i,j)=common_elements(a(i),b(j)) > } > } > > Is there an efficient, clean way to do the same job and give as an > output a matrix N_A x N_B such as that above? > > Thanks a lot for your help > > Regards > > Pietro > > ______________________________________________________________________ > > For information pertaining to Willis' email confidentiality and monitoring > policy, usage restrictions, or for specific company registration and > regulatory status information, please visit > http://www.willis.com/email_trailer.aspx > > We are now able to offer our clients an encrypted email capability for secure > communication purposes. If you wish to take advantage of this service or > learn more about it, please let me know or contact your Client Advocate for > full details. ~W67897 > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Jim Holtman Data Munger Guru What is the problem that you are trying to solve? Tell me what you want to do, not how you want to do it. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
