chunkedMap: Applies a Function on Each Chunk of a File-Backed Matrix
In BGData: A Suite of Packages for Analysis of Big Genomic Data

chunkedMap

R Documentation

Applies a Function on Each Chunk of a File-Backed Matrix

Description

Similar to lapply, but designed for file-backed matrices. The function brings chunks of an object into physical memory by taking subsets, and applies a function on them. If nCores is greater than 1, the function will be applied in parallel using mclapply. In that case the subsets of the object are taken on the slaves.

Usage

chunkedMap(X, FUN, i = seq_len(nrow(X)), j = seq_len(ncol(X)),
  chunkBy = 2L, chunkSize = 5000L, nCores = getOption("mc.cores",
  2L), verbose = FALSE, ...)

Arguments

`X`	A file-backed matrix, typically the genotypes of a `BGData` object.
`FUN`	The function to be applied on each chunk.
`i`	Indicates which rows of `X` should be used. Can be integer, boolean, or character. By default, all rows are used.
`j`	Indicates which columns of `X` should be used. Can be integer, boolean, or character. By default, all columns are used.
`chunkBy`	Whether to extract chunks by rows (1) or by columns (2). Defaults to columns (2).
`chunkSize`	The number of rows or columns of `X` that are brought into physical memory for processing per core. If `NULL`, all elements in `i` or `j` are used. Defaults to 5000.
`nCores`	The number of cores (passed to `mclapply`). Defaults to the number of cores as detected by `detectCores`.
`verbose`	Whether progress updates will be posted. Defaults to `FALSE`.
`...`	Additional arguments to be passed to the `apply` like function.

Examples

# Restrict number of cores to 1 on Windows
if (.Platform$OS.type == "windows") {
    options(mc.cores = 1)
}

# Load example data
bg <- BGData:::loadExample()

# Compute column sums of each chunk
chunkedMap(X = geno(bg), FUN = colSums)

BGData documentation built on March 31, 2023, 6:57 p.m.