readTableIndex {R.utils}R Documentation

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 (http://www.braju.com/R/)

See Also

readTable().

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)

[Package R.utils version 1.1.1 Index]