R: Map a function over a file by chunks

chunk.map {iotools} | R Documentation

## Map a function over a file by chunks

### Description

A wrapper around the core iotools functions to easily apply a function over chunks of a large file. Results can be either written to a file or returned as an internal list.

### Usage

    chunk.map(input, output = NULL, formatter = .default.formatter,
              FUN, key.sep = NULL, max.line = 65536L,
              max.size = 33554432L, output.sep = ",", output.nsep = "\t",
              output.keys = FALSE, skip = 0L, ...)

### Arguments

`input` | an input connection or character vector describing a local file.
`output` | an optional output connection or character vector describing a local file. If `NULL`, the results are returned internally as a list.
`formatter` | a function that takes raw input and produces the input given to `FUN`
`FUN` | a user provided function to map over the chunks. The result of FUN is either wrapper in a list item, when `output` is `NULL`, or written to the output file using `as.output`
`key.sep` | optional key separator given to `chunk.reader`
`max.line` | maximum number of lines given to `chunk.reader`
`max.size` | maximum size of a block as given to `read.chunk`
`output.sep` | single character giving the field separator in the output.
`output.nsep` | single character giving the key separator in the output.
`output.keys` | logical. Whether as.output should interpret row names as keys.
`skip` | integer giving the number of lines to strip off the input before reading. Useful when the input contains a row a column headers
`...` | additional parameters to pass to `FUN`

### Value

A list of results when `output` is `NULL`; otherwise no output is returned.

### Author(s)

Taylor Arnold

[Package iotools version 0.3-1 Index]