filehashSQLite-class {filehashSQLite} | R Documentation |
Create a 'filehash' database using SQLite as the backend
The "filehashSQLite"
class represents a "filehash"
key-value database using the SQLite DBM as the backend. Objects are
stored in a single SQLite database table along with their keys.
Objects can be created by calls of the form
new("filehashSQLite", ...)
. More likely, one will use the
functions dbCreate
and dbInit
from the filehash
package.
datafile
:dbcon
:"SQLiteConnection"
, a SQLite connectionname
:
Class "filehash"
, directly.
signature(db = "filehashSQLite", key =
"character")
: delete a key-value pair from the database signature(db = "filehashSQLite", key =
"character")
: check the existence of a specific key or vector
of keys signature(db = "filehashSQLite", key =
"character")
: retrieve the value associated with a specific key signature(db = "filehashSQLite", key =
"character")
: insert a key-value pair signature(db = "filehashSQLite")
: return
character vector of keys currently stored in the database signature(db = "filehashSQLite")
: delete the
entire database signature(db = "filehashSQLite", key =
"character")
: return (as a named list) the values associated
with a vector of keys
"filehashSQLite"
databases have a "["
method that can be
used to extract multiple elements in an efficient manner. The return
value is a list with names equal to the keys passed to "["
.
If there are keys passed to "["
that do not exist in the
database, a warning is given.
The "SQLite"
format for filehash
uses an ASCII
serialization of the data which could result in some rounding error
for floating point numbers.
Note that if you use keys that are numbers coerced to character vectors, then you may have trouble with them being coerced to numeric. The SQLite database will see these key values and automatically convert them to numbers.
Roger D. Peng
library(filehashSQLite) dbCreate("myTestDB", type = "SQLite") db <- dbInit("myTestDB", type = "SQLite") set.seed(100) db$a <- rnorm(100) db$b <- "a character element" with(db, mean(a)) cat(db$b, "\n")