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)

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().

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).

Note

The mat2triplet() utility was created to be a more efficient and more predictable substitute for summary(<sparseMatrix>). UseRs have wrongly expected the latter to return a data frame with columns i and j which however is wrong for a "diagonalMatrix".

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))