filehash-class {filehash} | R Documentation |
These functions form the interface for a simple file-based key-value database (i.e. hash table).
Objects can be created by calls of the form new("filehash", ...)
.
name
:"character"
, name of the
database.datafile
:meta
:dbDelete
function is for deleting
elements, but for the "DB1"
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."RDS"
type databases, there is a safe
option
(defaults to TRUE
) which allows the user to insert objects
somewhat more safely (objects should not be lost in the event of
an interrupt).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 extensively and so should be considered
experimental. dbReorganize
is not needed when using
the "RDS"
format.with
to be used with "filehash"
objects much like it can be used with lists or data frames[[
operator much like a list or environment, but only character
indices are allowed$
operator much like with a list or environmentlapply
with lists; a list is
returned.Roger D. Peng rpeng@jhsph.edu
dbCreate("myDB") ## Create database 'myDB' db <- dbInit("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) ## "b" with(db, mean(b))