spMatrix {Matrix} | R Documentation

## Sparse Matrix Constructor From Triplet

### Description

User friendly construction of a sparse matrix (inheriting from class `TsparseMatrix`) from the triplet representation.

### Usage

    spMatrix(nrow, ncol, i = integer(), j = integer(), x = numeric())

### Arguments

`nrow, ncol` | integers specifying the desired number of rows and columns.
`i,j` | integer vectors of the same length specifying the locations of the non-zero (or non-`TRUE`) entries of the matrix.
`x` | atomic vector of the same length as `i` and `j`, specifying the values of the non-zero entries.

### Value

A sparse matrix in triplet form, as an R object inheriting from both `TsparseMatrix` and `generalMatrix`.
The matrix M will have `M[i[k], j[k]] == x[k]`, for k = 1,2,..., n, where `n = length(i)` and `M[ i', j' ] == 0` for all other pairs (i',j').

### See Also

`Matrix(*, sparse=TRUE)` for the more usual constructor of such matrices; similarly, `sparseMatrix` which is a bit more general than `spMatrix()` and returns a `CsparseMatrix` which is often slightly more desirable. Further, `bdiag` and `Diagonal` for (block-)diagonal matrix constructors.

Consider `TsparseMatrix` and similar class definition help files.

### Examples

    ## simple example
    A <- spMatrix(10,20, i = c(1,3:8),
                         j = c(2,9,6:10),
                         x = 7 * (1:7))
    A # a "dgTMatrix"
    summary(A)
    str(A) # note that *internally* 0-based indices (i,j) are used

    L <- spMatrix(9, 30, i = rep(1:9, 3), 1:27,
                  (1:27) %% 4 != 1)
    L # an "lgTMatrix"

    ### This is a useful utility, to be used for experiments :

     rSpMatrix <- function(nrow, ncol, nnz,
                           rand.x = function(n) round(rnorm(nnz), 2))
     {
         ## Purpose: random sparse matrix
         ## --------------------------------------------------------------
         ## Arguments: (nrow,ncol): dimension
         ##          nnz  :  number of non-zero entries
         ##         rand.x:  random number generator for 'x' slot
         ## --------------------------------------------------------------
         ## Author: Martin Maechler, Date: 14.-16. May 2007
         stopifnot((nnz <- as.integer(nnz)) >= 0,
                   nrow >= 0, ncol >= 0,
                   nnz <= nrow * ncol)
         spMatrix(nrow, ncol,
                  i = sample(nrow, nnz, replace = TRUE),
                  j = sample(ncol, nnz, replace = TRUE),
                  x = rand.x(nnz))
     }

     M1 <- rSpMatrix(100000, 20, nnz = 200)
     summary(M1)

[Package Matrix version 0.999375-33 Index]