thank you, Petr.
This is exactly what I'm looking for in my post.
An related question can be how to get an arbitrary weight, say if row1
and row 2 have 1 common value 1, then assign a weight 10, if row 1 and
row 2 have 2 common value 1, then assign a weight 12. I'm not so sure
how to expand your method.
Really need to refresh my linear algebra;-)
regards,
cal@cowbo
On 6/14/12, Petr Savicky savi...@cs.cas.cz wrote:
On Thu, Jun 14, 2012 at 01:11:45PM +, G. Dai wrote:
Dear Rlisters,
I'm writing to ask how to manipulate a matrix or dataframe in a specific
way.
To elaborate, let's consider an example. Assume we have the following
3 by 4 matrix A with elements either 0 or 1,
0 1 1 0
1 0 1 1
0 0 0 1
From the original matrix A, I'd like to generate a new matrix B
satisfing
1) B is initially set to be equal to A, and then
2) Each row of B is a weighted sum of rows of A
3) The weight is given by the number of common 1 shared by the rows.
For row 1:
it has one common 1 with row 2, thus the weight is 1;
it has zero common 1 with row 3, thus the weight is 0;
For row 2:
it has one common 1 with row 1, thus the weight is 1;
it has one common 1 with row 3, thus the weight is 1;
For row 3:
it has zero common 1 with row 1, thus the weight is 0;
it has one common 1 with row 2, thus the weight is 1;
4) In this way, the new matrix B is
1 1 2 1
1 1 2 2
1 0 1 2
Hi.
If i understand correctly, each row of B is obtained from the
corresponding row of A by adding mutliples of other rows using
the weights as described. Try the following.
a - rbind(
c(0, 1, 1, 0),
c(1, 0, 1, 1),
c(0, 0, 0, 1))
w - a %*% t(a)
diag(w) - 1
w %*% a
[,1] [,2] [,3] [,4]
[1,]1121
[2,]1122
[3,]1012
The entries of w are the weights except of the diagonal, which
is all ones, since each row of A contributes to the same row of B
with weight one. Is this, what you are looking for?
Petr Savicky.
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