initExtension {RSQLite} | R Documentation |
Add useful extension functions
Description
Several extension functions are included in the RSQLite package.
When enabled via initExtension()
, these extension functions can be used in
SQL queries.
Extensions must be enabled separately for each connection.
Usage
initExtension(db, extension = c("math", "regexp", "series", "csv"))
Arguments
db |
A |
extension |
The extension to load. |
Details
The "math"
extension functions are written by Liam Healy and made available
through the SQLite website (https://www.sqlite.org/contrib).
This package contains a slightly modified version of the original code.
See the section "Available functions in the math extension" for details.
The "regexp"
extension provides a regular-expression matcher for POSIX
extended regular expressions,
as available through the SQLite source code repository
(https://sqlite.org/src/file?filename=ext/misc/regexp.c).
SQLite will then implement the A regexp B
operator,
where A
is the string to be matched and B
is the regular expression.
The "series"
extension loads the table-valued function generate_series()
,
as available through the SQLite source code repository
(https://sqlite.org/src/file?filename=ext/misc/series.c).
The "csv"
extension loads the function csv()
that can be used to create
virtual tables,
as available through the SQLite source code repository
(https://sqlite.org/src/file?filename=ext/misc/csv.c).
Available functions in the math extension
- Math functions
acos, acosh, asin, asinh, atan, atan2, atanh, atn2, ceil, cos, cosh, cot, coth, degrees, difference, exp, floor, log, log10, pi, power, radians, sign, sin, sinh, sqrt, square, tan, tanh
- String functions
charindex, leftstr, ltrim, padc, padl, padr, proper, replace, replicate, reverse, rightstr, rtrim, strfilter, trim
- Aggregate functions
stdev, variance, mode, median, lower_quartile, upper_quartile
Examples
library(DBI)
db <- RSQLite::datasetsDb()
# math
RSQLite::initExtension(db)
dbGetQuery(db, "SELECT stdev(mpg) FROM mtcars")
sd(mtcars$mpg)
# regexp
RSQLite::initExtension(db, "regexp")
dbGetQuery(db, "SELECT * FROM mtcars WHERE carb REGEXP '[12]'")
# series
RSQLite::initExtension(db, "series")
dbGetQuery(db, "SELECT value FROM generate_series(0, 20, 5);")
dbDisconnect(db)
# csv
db <- dbConnect(RSQLite::SQLite())
RSQLite::initExtension(db, "csv")
# use the filename argument to mount CSV files from disk
sql <- paste0(
"CREATE VIRTUAL TABLE tbl USING ",
"csv(data='1,2', schema='CREATE TABLE x(a INT, b INT)')"
)
dbExecute(db, sql)
dbGetQuery(db, "SELECT * FROM tbl")