Matrix (version 1.5-1)

mat2triplet: Map Matrix to its Triplet Representation

Description

From an R object coercible to "TsparseMatrix", typically a (sparse) matrix, produce its triplet representation which may collapse to a “Duplet” in the case of binary aka pattern, such as "nMatrix" objects.

Usage

mat2triplet(x, uniqT = FALSE)

Value

A list, typically with three components,

i

vector of row indices for all non-zero entries of x

i

vector of columns indices for all non-zero entries of x

x

vector of all non-zero entries of x; exists only when as(x, "TsparseMatrix") is not a "nsparseMatrix".

Note that the order of the entries is determined by the coercion to "TsparseMatrix" and hence typically with increasing j (and increasing i within ties of j).

Arguments

x

any R object for which as(x, "TsparseMatrix") works; typically a matrix of one of the Matrix package matrices.

uniqT

logical indicating if the triplet representation should be ‘unique’ in the sense of uniqTsparse().

See Also

The summary() method for "sparseMatrix", summary,sparseMatrix-method.

mat2triplet() is conceptually the inverse function of spMatrix and (one case of) sparseMatrix.

Examples

if(FALSE) ## The function is defined (don't redefine here!), simply as
mat2triplet <- function(x, uniqT = FALSE) {
    T <- as(x, "TsparseMatrix")
    if(uniqT && anyDuplicatedT(T)) T <- .uniqTsparse(T)
    if(is(T, "nsparseMatrix"))
         list(i = T@i + 1L, j = T@j + 1L)
    else list(i = T@i + 1L, j = T@j + 1L, x = T@x)
}

i <- c(1,3:8); j <- c(2,9,6:10); x <- 7 * (1:7)
(Ax <- sparseMatrix(i, j, x = x)) ##  8 x 10 "dgCMatrix"
str(trA <- mat2triplet(Ax))
stopifnot(i == sort(trA$i),  sort(j) == trA$j,  x == sort(trA$x))

D <- Diagonal(x=4:2)
summary(D)
str(mat2triplet(D))