R.utils: readTableIndex – R documentation

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readTableIndex

Reads a single column from file in table format

Description

Reads a single column from file in table format, which can then be used as a index-to-row (look-up) map for fast access to a subset of rows using readTable().

Usage

## Default S3 method:
readTableIndex(..., indexColumn=1, colClass="character", verbose=FALSE)

Arguments

`indexColumn`	An single `integer` of the index column.
`colClass`	A single `character` specifying the class of the index column.
`...`	Arguments passed to `readTable`() used internally.
`verbose`	A `logical` or a `Verbose` object.

Value

Returns a vector.

Author(s)

Henrik Bengtsson

Examples

## Not run: 
   # File containing data table to be access many times
   filename <- "somefile.txt"

   # Create a look-up index
   index <- readTableIndex(filename)

   # Keys of interest
   keys <- c("foo", "bar", "wah")

   # Read only those keys and do it fast
   df <- readTable(filename, rows=match(keys, index))

## End(Not run)

R.utils

Various Programming Utilities

v2.10.1

LGPL (>= 2.1)

Authors

Henrik Bengtsson [aut, cre, cph]

Initial release