RPresto is a DBI-based adapter for the open source distributed SQL query engine Presto for running interactive analytic queries.
RPresto is both on CRAN and github. For the CRAN version, you can use
You can install the github development version via
The standard DBI approach works with RPresto:
library('DBI')
con <- dbConnect(
RPresto::Presto(),
host='http://localhost',
port=7777,
user=Sys.getenv('USER'),
schema='<schema>',
catalog='<catalog>',
source='<source>'
)
res <- dbSendQuery(con, 'SELECT 1')
# dbFetch without arguments only returns the current chunk, so we need to
# loop until the query completes.
while (!dbHasCompleted(res)) {
chunk <- dbFetch(res)
print(chunk)
}
res <- dbSendQuery(con, 'SELECT CAST(NULL AS VARCHAR)')
# Due to the unpredictability of chunk sizes with presto, we do not support
# custom number of rows
# testthat::expect_error(dbFetch(res, 5))
# To get all rows using dbFetch, pass in a -1 argument
print(dbFetch(res, -1))
# An alternative is to use dbGetQuery directly
# `source` for iris.sql()
source(system.file('tests', 'testthat', 'utilities.R', package='RPresto'))
iris <- dbGetQuery(con, paste("SELECT * FROM", iris.sql()))
dbDisconnect(con)
We also include dplyr integration.
library(dplyr)
db <- src_presto(
host='http://localhost',
port=7777,
user=Sys.getenv('USER'),
schema='<schema>',
catalog='<catalog>',
source='<source>'
)
# Assuming you have a table like iris in the database
iris <- tbl(db, 'iris')
iris %>%
group_by(species) %>%
summarise(mean_sepal_length = mean(as(sepal_length, 0.0))) %>%
arrange(species) %>%
collect()
Presto exposes its interface via a REST based API1. We utilize the httr package to make the API calls and use jsonlite to reshape the data into a data.frame
. Note that as of now, only read operations are supported.
RPresto has been tested on Presto 0.100.
RPresto is BSD-licensed.
[1] See https://github.com/prestodb/presto/wiki/HTTP-Protocol for a description of the API.