Dear David, and R-users,
thanks for the response. I'll do my best to describe the context.
My data consists in two matrices, D and T. The former provides simple
values, the latter is a Boolean matrix. The number of rows in D is equal
to the number of columns in T.
My aim is to construct a larger matrix which is made up of sum(T)
diagonal matrices constructed from the rows of D, and placed according
to a structure given by a transformation of T.
Whereas the positions of the columns in which T is equal to 1 informs
about the placement of the diagonal matrices, the positions of the rows
in which T is equal to 1 informs about which row to take from D in order
to create these diagonal matrices.
In the code below (corrected in the last line with respect to the
previous version, sorry), I first created the matrices D and T. Then I
built a 0/1 matrix (M0) that presents the structure of the final
block-matrix made up of diagonal matrices, and, by Kronecker product, a
matrix with the final 0/1 structure is constructed, M.
Using the rows in which T is equal to 1, I select the values from D and
place in the matrix M, where such matrix is equal to 1.
It's a long explanation and I could not find a better way to program
(and explain) it.
Thanks for you help,
Giancarlo
## data in matrices
D - matrix(1:15, 3, 5)
T - matrix(0, 3, 3)
T[c(2,4,6,8)] - 1
## the col of T equal to 1 gives the position
wr - which(T==1, arr.ind=TRUE)[,2]
## we aim to sum(T) diagonal matrices
wc - 1:sum(T)
## structure: how to place the diagonal matrices
M0 - matrix(0, nrow(T), sum(T))
M0[cbind(wr,wc)] - 1
## number of columns
m - ncol(D)
## final 0/1 matrix
M - kronecker(M0, diag(m))
## the row of T equal to 1 gives which rows to take from D
pos - which(T==1, arr.ind=TRUE)[,1]
## filling up with data
M[M!=0] - t(D[pos,])
On 29/01/2014 01:49, David Winsemius wrote:
On Jan 27, 2014, at 8:04 AM, Carlo Giovanni Camarda wrote:
Dear R-users,
I would like to know whether you know some trick for skipping some of
the steps in the example below (especially the last step in a way that
would make easier to be written succinctly in a text).
I could try to explain in words the whole process, but I'm sure the code
below would be clearer.
After looking at the code and output, I must disagree. The lack of any
response from the rest of the readership suggests to me that I am not the
only one who thinks a natural language description of the context and goals
for this effort would help.
Thanks in advance for your help,
Giancarlo
## data in matrices
D - matrix(1:15, 3, 5)
T - matrix(0, 3, 3)
T[c(2,4,6,8)] - 1
## how to place the diag matrices of each row
M0 - matrix(0, nrow(T), sum(T))
wr - which(T==1, arr.ind=TRUE)[,2]
wc - 1:ncol(M0)
M0[cbind(wr,wc)] - 1
## number of columns
m - ncol(D)
## non-zero positions
M - kronecker(M0, diag(m))
## which rows to take
pos - which(T==1, arr.ind=TRUE)[,1]
## filling up with data
M[M!=0] - t(D[wr,])
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David Winsemius
Alameda, CA, USA
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