From: Adaikalavan Ramasamy (ramasamy@stats.ox.ac.uk)
Date: Mon 02 Sep 2002 - 16:41:25 EST
Message-id: <003201c2524b$c2905960$461401a3@stats.ox.ac.uk>
Try either this or crossprod() ...
> x%*%t(x)
[,1] [,2] [,3] [,4]
[1,] 2 0 2 2
[2,] 0 2 0 1
[3,] 2 0 2 2
[4,] 2 1 2 4
The above is "like" distance matrix. eg B and D have only one "1" in common.
Notice the symmetry about the diagonal.
The diagonals are not so useful as they tell you how many "1"'s A, B, C, D
have in them.
----- Original Message -----
From: To: r-help@stat.math.ethz.ch
Sent: Saturday, August 31, 2002 6:22 AM
Subject: [R] Counting elements in 2 rows of a matrix
Dear R-users:
Sorry to bother so late with this question, which surely has simple
answer. I'm working with matrices that contain either "1" or "0", for
example:
[,1] [,2] [,3] [,4] [,5]
A 1 0 1 0 0
B 0 1 0 1 0
C 1 0 1 0 0
D 1 1 1 0 1
I want to count the number of "1" common to, say, A and B, the number of
"1" that appear only in A and the number of "1" that appear only in B.
Please let me know if there's a simple way of doing this without the
complicated for...next loops that have come across my mind.
Fredy Mejía
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