dgTMatrix-class: Sparse matrices in triplet form

In Matrix: Sparse and Dense Matrix Classes and Methods

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 in 0:(nrow(.)-1).

j:

integer column indices of non-zero entries. Must be the same length as slot i and 0-based as well, i.e., in 0:(ncol(.)-1).

x:

numeric vector - the (non-zero) entry at position (i,j). Must be the same length as slot i. If an index pair occurs more than once, the corresponding values of slot x 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 of x using the levelplot function

t

signature(x = "dgTMatrix"): returns the transpose of x

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)

Matrix documentation built on Oct. 19, 2024, 1:08 a.m.