SparseArraySeed-class {DelayedArray} | R Documentation

## SparseArraySeed objects

### Description

SparseArraySeed objects are used internally to support block processing of array-like objects.

### Usage

    ## Constructor function:
    SparseArraySeed(dim, nzindex=NULL, nzdata=NULL, dimnames=NULL, check=TRUE)

    ## Getters (in addition to dim(), length(), and dimnames()):
    nzindex(x)
    nzdata(x)
    sparsity(x)

    ## Two low-level utilities:
    dense2sparse(x)
    sparse2dense(sas)

### Arguments

`dim` | The dimensions (specified as an integer vector) of the SparseArraySeed object to create.
`nzindex` | A matrix containing the array indices of the nonzero data. This must be an integer matrix like one returned by `base::arrayInd`, that is, with `length(dim)` columns and where each row is an n-uplet representing an array index.
`nzdata` | A vector of length `nrow(nzindex)` containing the nonzero data.
`dimnames` | The dimnames of the object to be created. Must be `NULL` or a list of length the number of dimensions. Each list element must be either `NULL` or a character vector along the corresponding dimension.
`check` | Should the object be validated upon construction?
`x` | A SparseArraySeed object for the `nzindex`, `nzdata`, and `sparsity` getters. An array-like object for `dense2sparse`.
`sas` | A SparseArraySeed object.

### Value

- For `SparseArraySeed()`: A SparseArraySeed instance.

- For `nzindex()`: The matrix containing the array indices of the nonzero data.

- For `nzdata()`: The vector of nonzero data.

- For `sparsity()`: The number of zero-valued elements in the implicit array divided by the total number of array elements (a.k.a. the length of the array).

- For `dense2sparse()`: A SparseArraySeed instance.

- For `sparse2dense()`: An ordinary array.

### See Also

- SparseArraySeed-utils for native operations on SparseArraySeed objects.

- The `read_block` function.

- `blockApply` and family for convenient block processing of an array-like object.

- `extract_array`.

- DelayedArray objects.

- `arrayInd` in the base package.

- array objects in base R.

### Examples

    ## ---------------------------------------------------------------------
    ## EXAMPLE 1
    ## ---------------------------------------------------------------------
    dim1 <- 5:3
    nzindex1 <- Lindex2Mindex(sample(60, 8), 5:3)
    nzdata1 <- 11.11 * seq_len(nrow(nzindex1))
    sas1 <- SparseArraySeed(dim1, nzindex1, nzdata1)

    dim(sas1)        # the dimensions of the implicit array
    length(sas1)     # the length of the implicit array
    nzindex(sas1)
    nzdata(sas1)
    type(sas1)
    sparsity(sas1)

    sparse2dense(sas1)
    as.array(sas1)   # same as sparse2dense(sas1)

    ## Not run:
    as.matrix(sas1)  # error!

    ## End(Not run)
    ## ---------------------------------------------------------------------
    ## EXAMPLE 2
    ## ---------------------------------------------------------------------
    m2 <- matrix(c(5:-2, rep.int(c(0L, 99L), 11)), ncol=6)
    sas2 <- dense2sparse(m2)
    class(sas2)
    dim(sas2)
    length(sas2)
    nzindex(sas2)
    nzdata(sas2)
    type(sas2)
    sparsity(sas2)

    stopifnot(identical(sparse2dense(sas2), m2))

    as.matrix(sas2)  # same as sparse2dense(sas2)

    t(sas2)
    stopifnot(identical(as.matrix(t(sas2)), t(as.matrix(sas2))))

    ## ---------------------------------------------------------------------
    ## COERCION FROM/TO dgCMatrix OR lgCMatrix OBJECTS
    ## ---------------------------------------------------------------------
    ## dgCMatrix and lgCMatrix objects are defined in the Matrix package.

    M2 <- as(sas2, "dgCMatrix")
    stopifnot(identical(M2, as(m2, "dgCMatrix")))

    sas2b <- as(M2, "SparseArraySeed")
    ## 'sas2b' is the same as 'sas2' except that 'nzdata(sas2b)' has
    ## type "double" instead of "integer":
    stopifnot(all.equal(sas2b, sas2))
    typeof(nzdata(sas2b))  # double
    typeof(nzdata(sas2))   # integer

    m3 <- m2 == 99  # logical matrix
    sas3 <- dense2sparse(m3)
    class(sas3)
    type(sas3)
    M3 <- as(sas3, "lgCMatrix")
    stopifnot(identical(M3, as(m3, "lgCMatrix")))

    sas3b <- as(M3, "SparseArraySeed")
    stopifnot(identical(sas3, sas3b))

    ## ---------------------------------------------------------------------
    ## SEED CONTRACT
    ## ---------------------------------------------------------------------
    ## SparseArraySeed objects comply with the "seed contract".
    ## In particular they support extract_array():
    extract_array(sas1, list(c(5, 3:2, 5), NULL, 3))

    ## See '?extract_array' for more information about the "seed contract".

    ## This means that they can be wrapped in a DelayedArray object:
    A1 <- DelayedArray(sas1)
    A1

    ## A big very sparse DelayedMatrix object:
    nzindex4 <- cbind(sample(25000, 600000, replace=TRUE),
                      sample(195000, 600000, replace=TRUE))
    nzdata4 <- runif(600000)
    sas4 <- SparseArraySeed(c(25000, 195000), nzindex4, nzdata4)
    sparsity(sas4)

    M4 <- DelayedArray(sas4)
    M4
    colSums(M4[ , 1:20])

[Package DelayedArray version 0.16.3 Index]