fdply: Read some chunks from a file into a 'data.table'
In fplyr: Apply Functions to Blocks of Files

View source: R/fdply.R

fdply

R Documentation

Read some chunks from a file into a `data.table`

Description

This function is useful to quickly glance at a big chunked file. It is similar to the head() function, except that it does not read the first few lines, but rather the first few blocks of the file. By default, only the first block will be read; it is not advisable to read a large number of blocks in this way because they may occupy a lot of memory. The blocks are saved to a data.table. See ?fplyr for the definitions of chunked file and block.

Usage

fdply(
  input,
  nblocks = 1,
  key.sep = "\t",
  sep = "\t",
  skip = 0,
  colClasses = NULL,
  header = TRUE,
  stringsAsFactors = FALSE,
  select = NULL,
  drop = NULL,
  col.names = NULL,
  parallel = 1
)

Arguments

`input`	Path of the input file.
`nblocks`	The number of blocks to read.
`key.sep`	The character that delimits the first field from the rest.
`sep`	The field delimiter (often equal to `key.sep`).
`skip`	Number of lines to skip at the beginning of the file
`colClasses`	Vector or list specifying the class of each field.
`header`	Whether the file has a header.
`stringsAsFactors`	Whether to convert strings into factors.
`select`	The columns (names or numbers) to be read.
`drop`	The columns (names or numbers) not to be read.
`col.names`	Names of the columns.
`parallel`	Number of cores to use.