# [R] comparing row by row in matrix

Huntsinger, Reid reid_huntsinger at merck.com
Tue Mar 26 20:47:04 CET 2002

```I don't know the Russell-Rao coefficient but maybe this will help:

You can compute the number of times y and x are both 1 (that's what your
function f does) by counting 1s in y*x, i.e., sum(y*x), aka t(y)%*%x.
Ordinary matrix multiplication does this row-by-column, so if M and N are
two binary matrices, M%*%t(N) will have (i,j) entry equal to the count of 1s
in common to row i of M and row j of N.

Hope I've understood the problem correctly.

Reid Huntsinger

-----Original Message-----
From: Petra Steiner [mailto:steinep at uni-muenster.de]
Sent: Tuesday, March 26, 2002 2:08 PM
To: r-help at stat.math.ethz.ch
Subject: [R] comparing row by row in matrix

Hello,

and thanks for the two responses to my questions on binary matrixes, which
showed me that the functions I needed do not exist.

To get a distance matrix with the Russell-Rao-coefficient, I first have to
compare each row of a binary matrix with each row and count how many
elements are
a. equal
and
b. 1.

by
f <- function(x,y) (sum(x == 1& y == x))

Now how can I iterate this over a matrix without a loop? I think apply etc.
will not work in this case.

Thanks for any help.

Regards,
Petra

-
---------------------------------------------------
Petra Steiner
Arbeitsbereich Linguistik
Universitaet Muenster
Huefferstrasse 27
48149  Muenster

Tel: 0251 / 83 39442
petra at marley.uni-muenster.de
http://santana.uni-muenster.de/~petra/

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