colCollapse {DelayedMatrixStats} | R Documentation

## Extracts one cell per row (column) from a matrix

### Description

Extracts one cell per row (column) from a matrix. The implementation is optimized for memory and speed.

### Usage

    colCollapse(x, idxs, cols = NULL, dim. = dim(x), ...)

    rowCollapse(x, idxs, rows = NULL, dim. = dim(x), ...)

    ## S4 method for signature 'DelayedMatrix'
    colCollapse(x, idxs, cols = NULL, dim. = dim(x),
      force_block_processing = FALSE, ...)

    ## S4 method for signature 'DelayedMatrix'
    rowCollapse(x, idxs, rows = NULL, dim. = dim(x),
      force_block_processing = FALSE, ...)

### Arguments

`x` | A NxK DelayedMatrix.
`idxs` | An index `vector` of (maximum) length N (K) specifying the columns (rows) to be extracted.
`cols` | A `vector` indicating subset of rows (and/or columns) to operate over. If `NULL`, no subsetting is done.
`dim.` | An `integer` `vector` of length two specifying the dimension of `x`, also when not a `matrix`.
`...` | Additional arguments passed to specific methods.
`rows` | A `vector` indicating subset of rows (and/or columns) to operate over. If `NULL`, no subsetting is done.
`force_block_processing` | `FALSE` (the default) means that a seed-aware, optimised method is used (if available). This can be overridden to use the general block-processing strategy by setting this to `TRUE` (typically not advised). The block-processing strategy loads one or more (depending on `getOption("DelayedArray.block.size")`) columns (`colFoo()`) or rows (`rowFoo()`) into memory as an ordinary base::array.

### Value

Returns a `vector` of length N (K).

### See Also

Matrix indexing to index elements in matrices and arrays, cf. `[`().

### Examples

    # A DelayedMatrix with a 'matrix' seed
    dm_matrix <- DelayedArray(matrix(c(rep(1L, 5),
                                       as.integer((0:4) ^ 2),
                                       seq(-5L, -1L, 1L)),
                                     ncol = 3))
    # A DelayedMatrix with a 'HDF5ArraySeed' seed
    # NOTE: Requires that the HDF5Array package is installed
    library(HDF5Array)
    dm_HDF5 <- writeHDF5Array(matrix(c(rep(1L, 5),
                                       as.integer((0:4) ^ 2),
                                       seq(-5L, -1L, 1L)),
                                     ncol = 3))

    # Extract the 4th row as a vector
    # NOTE: An ordinary vector is returned regardless of the backend of
    #       the DelayedMatrix object
    colCollapse(dm_matrix, 4)
    colCollapse(dm_HDF5, 4)

    # Extract the 2nd column as a vector
    # NOTE: An ordinary vector is returned regardless of the backend of
    #       the DelayedMatrix object
    rowCollapse(dm_matrix, 2)
    rowCollapse(dm_HDF5, 2)

[Package DelayedMatrixStats version 1.0.3 Index]