[R] RE: Counting elements in 2 rows of a matrix

[Adaikalavan Ramasamy]

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 at 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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