R: Extracts one cell per row (column) from a matrix

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 `\link[DelayedArray]{getAutoBlockSize}()`) columns (`colFoo()`) or rows (`rowFoo()`) into memory as an ordinary base::array.

Value

Returns a vector of length N (K).

Author(s)

Peter Hickey

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 1.10.1 Index]