filehash-class {filehash}R Documentation

Class "filehash"

Description

These functions form the interface for a simple file-based hash table.

Objects from the Class

Objects can be created by calls of the form new("filehash", ...).

Slots

name:
Object of class "character", name of the database.

Additional slots for "filehashDB"

datafile:
Object of class "character", full path to the database file.
mapfile:
Object of class "character", full path to the index file.

Additional slots for "filehashRDS"

dbDir:
Directory where files are stored.

Methods

dbDelete
signature(db = "filehash", key = "character"): The dbDelete function is for deleting elements, but for the "DB" format all it does is remove the key from the lookup table. The actual data are still in the database (but inaccessible). If you reinsert data for the same key, the new data are simply appended on to the end of the file. Therefore, it's possible to have multiple copies of data lying around after a while, potentially making the database file big. The "RDS" format does not have this problem.
dbExists
signature(db = "filehash", key = "character"): check to see if a key exists.
dbFetch
signature(db = "filehash", key = "character"): retrieve the value associated with a given key.
dbInsert
signature(db = "filehash", key = "character"): insert a key-value pair into the database. If that key already exists, its associated value is overwritten.
dbList
signature(db = "filehash"): list all keys in the database.
dbReorganize
signature(db = "filehashDB"): The dbReorganize function is there for the purpose of rewriting the database to remove all of the stale entries. Basically, this function creates a new copy of the database and then overwrites the old copy. This function has not been tested much and so should be considered experimental. dbReorganize is not needed when using the "RDS" format.
dbUnlink
delete an entire database from the disk
show
print method
with
allows with to be used with "filehash" objects much like it can be used with lists or data frames

Author(s)

Roger D. Peng rpeng@jhsph.edu

Examples

dbCreate("myDB")  ## Create files 'myDB.idx' and 'myDB.rdb'
db <- dbInitialize("myDB")
dbInsert(db, "a", 1:10)
dbInsert(db, "b", rnorm(1000))
dbExists(db, "b")  ## 'TRUE'

dbList(db)  ## c("a", "b")
dbDelete(db, "a")
dbList(db) ## "a"

with(db, mean(b))

[Package filehash version 0.4 Index]