Map Matrix to its Triplet Representation

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.

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 asUniqueT(byrow=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).

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

mat2triplet # simple definition
#> function (x, uniqT = FALSE) 
#> {
#>     T <- as(x, "TsparseMatrix")
#>     if (uniqT) 
#>         T <- asUniqueT(T, isT = TRUE)
#>     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)
#> }
#> <bytecode: 0x55f4e27edb18>
#> <environment: namespace:Matrix>

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"
#> 8 x 10 sparse Matrix of class "dgCMatrix"
#>                              
#> [1,] . 7 . . .  .  .  .  .  .
#> [2,] . . . . .  .  .  .  .  .
#> [3,] . . . . .  .  .  . 14  .
#> [4,] . . . . . 21  .  .  .  .
#> [5,] . . . . .  . 28  .  .  .
#> [6,] . . . . .  .  . 35  .  .
#> [7,] . . . . .  .  .  . 42  .
#> [8,] . . . . .  .  .  .  . 49
str(trA <- mat2triplet(Ax))
#> List of 3
#>  $ i: int [1:7] 1 4 5 6 3 7 8
#>  $ j: int [1:7] 2 6 7 8 9 9 10
#>  $ x: num [1:7] 7 21 28 35 14 42 49
stopifnot(i == sort(trA$i),  sort(j) == trA$j,  x == sort(trA$x))

D <- Diagonal(x=4:2)
summary(D)
#> 3 x 3 diagonal Matrix of class "ddiMatrix"
#>    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
#>     2.0     2.5     3.0     3.0     3.5     4.0 
str(mat2triplet(D))
#> List of 3
#>  $ i: int [1:3] 1 2 3
#>  $ j: int [1:3] 1 2 3
#>  $ x: num [1:3] 4 3 2