| nsparseMatrix-classes {Matrix} | R Documentation |
The nsparseMatrix class is a virtual class of sparse
“pattern” matrices, i.e., binary matrices conceptually
with TRUE/FALSE entries. Only the positions of the
elements that are TRUE are stored. These can be stored in the
“triplet” form (classes ngTMatrix, nsTMatrix, and
ntTMatrix which really contain pairs, not triplets) or in
compressed column-oriented form (classes ngCMatrix,
nsCMatrix, and ntCMatrix) or in compressed row-oriented
form (classes ngRMatrix, nsRMatrix, and
ntRMatrix). The second letter in the name of these non-virtual
classes indicates general, symmetric, or triangular.
Objects can be created by calls of the form new("ngCMatrix",
...) and so on. More frequently objects are created by coercion of
a numeric sparse matrix to the pattern form for use in
the symbolic analysis phase
of an algorithm involving sparse matrices. Such algorithms often
involve two phases: a symbolic phase wherein the positions of the
non-zeros in the result are determined and a numeric phase wherein the
actual results are calculated. During the symbolic phase only the
positions of the non-zero elements in any operands are of interest,
hence numeric sparse matrices can be treated as sparse pattern
matrices.
uplo:Object of class "character". Must be
either "U", for upper triangular, and "L", for lower
triangular. Present in the triangular and symmetric classes but not
in the general class.
diag:Object of class "character". Must be
either "U", for unit triangular (diagonal is all ones), or
"N" for non-unit. The implicit diagonal elements are not
explicitly stored when diag is "U". Present in the
triangular classes only.
p:Object of class "integer" of pointers, one
for each column (row), to the initial (zero-based) index of elements in
the column. Present in compressed column-oriented and compressed
row-oriented forms only.
i:Object of class "integer" of length nnzero
(number of non-zero elements). These are the row numbers for
each TRUE element in the matrix. All other elements are FALSE.
Present in triplet and compressed column-oriented forms only.
j:Object of class "integer" of length nnzero
(number of non-zero elements). These are the column numbers for
each TRUE element in the matrix. All other elements are FALSE.
Present in triplet and compressed column-oriented forms only.
Dim:Object of class "integer" - the dimensions
of the matrix.
signature(from = "dgCMatrix", to =
"ngCMatrix"), and many similar ones; typically you should
coerce to "nsparseMatrix" (or "nMatrix"). Note that
coercion to a sparse pattern matrix records all the potential
non-zero entries, i.e., explicit (“non-structural”) zeroes
are coerced to TRUE, not FALSE, see the example.
signature(x = "ngCMatrix"): returns the transpose
of x
signature(x = "lsparseMatrix"), semantically
equivalent to base function which(x, arr.ind);
for details, see the lMatrix class documentation.
the class dgCMatrix
(m <- Matrix(c(0,0,2:0), 3,5, dimnames=list(LETTERS[1:3],NULL)))
## ``extract the nonzero-pattern of (m) into an nMatrix'':
nm <- as(m, "nsparseMatrix") ## -> will be a "ngCMatrix"
str(nm) # no 'x' slot
nnm <- !nm # no longer sparse
(nnm <- as(nnm, "sparseMatrix"))# "lgCMatrix"
## consistency check:
stopifnot(xor(as( nm, "matrix"),
as(nnm, "matrix")))
## low-level way of adding "non-structural zeros" :
nnm@x[2:4] <- c(FALSE,NA,NA)
nnm
as(nnm, "nMatrix") # NAs *and* non-structural 0 |---> 'TRUE'
data(KNex)
nmm <- as(KNex $ mm, "ngCMatrix")
str(xlx <- crossprod(nmm))# "nsCMatrix"
stopifnot(isSymmetric(xlx))
image(xlx, main=paste("crossprod(nmm) : Sparse", class(xlx)))