| readTableIndex {R.utils} | R Documentation |
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().
## Default S3 method: readTableIndex(..., indexColumn=1, colClass="character", verbose=FALSE)
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. |
Returns a vector.
Henrik Bengtsson (http://www.braju.com/R/)
readTable().
## 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)