dgTMatrix-class {Matrix} | R Documentation |
Sparse matrices in triplet form
Description
The "dgTMatrix"
class is the class of sparse
matrices stored as (possibly redundant) triplets. The internal
representation is not at all unique, contrary to the one for class
dgCMatrix
.
Objects from the Class
Objects can be created by calls of the form
new("dgTMatrix", ...)
, but more typically via
spMatrix()
or sparseMatrix(*, repr = "T")
.
Slots
i
:integer
row indices of non-zero entries in 0-base, i.e., must be in0:(nrow(.)-1)
.j
:integer
column indices of non-zero entries. Must be the same length as sloti
and 0-based as well, i.e., in0:(ncol(.)-1)
.x
:numeric
vector - the (non-zero) entry at position(i,j)
. Must be the same length as sloti
. If an index pair occurs more than once, the corresponding values of slotx
are added to form the element of the matrix.Dim
:Object of class
"integer"
of length 2 - the dimensions of the matrix.
Methods
- +
signature(e1 = "dgTMatrix", e2 = "dgTMatrix")
- image
signature(x = "dgTMatrix")
: plots an image ofx
using thelevelplot
function- t
signature(x = "dgTMatrix")
: returns the transpose ofx
Note
Triplet matrices are a convenient form in which to construct sparse
matrices after which they can be coerced to
dgCMatrix
objects.
Note that both new(.)
and spMatrix
constructors
for "dgTMatrix"
(and other "TsparseMatrix"
classes) implicitly add x_k
's that belong to identical
(i_k, j_k)
pairs.
However this means that a matrix typically can be stored in more than
one possible "TsparseMatrix"
representations.
Use asUniqueT()
in order to ensure uniqueness of the
internal representation of such a matrix.
See Also
Class dgCMatrix
or the superclasses
dsparseMatrix
and
TsparseMatrix
; asUniqueT
.
Examples
m <- Matrix(0+1:28, nrow = 4)
m[-3,c(2,4:5,7)] <- m[ 3, 1:4] <- m[1:3, 6] <- 0
(mT <- as(m, "TsparseMatrix"))
str(mT)
mT[1,]
mT[4, drop = FALSE]
stopifnot(identical(mT[lower.tri(mT)],
m [lower.tri(m) ]))
mT[lower.tri(mT,diag=TRUE)] <- 0
mT
## Triplet representation with repeated (i,j) entries
## *adds* the corresponding x's:
T2 <- new("dgTMatrix",
i = as.integer(c(1,1,0,3,3)),
j = as.integer(c(2,2,4,0,0)), x=10*1:5, Dim=4:5)
str(T2) # contains (i,j,x) slots exactly as above, but
T2 ## has only three non-zero entries, as for repeated (i,j)'s,
## the corresponding x's are "implicitly" added
stopifnot(nnzero(T2) == 3)