R.utils (version 1.9.7)

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

## S3 method for class 'default':
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.

See Also

readTable().

Examples

# 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))