isabella232 / rpresto

DBI-based adapter for Presto for the statistical programming language R.

RPresto

RPresto is a DBI-based adapter for the open source distributed SQL query engine Presto for running interactive analytic queries.

Installation

RPresto is both on CRAN and github. For the CRAN version, you can use

install.packages('RPresto')

You can install the github development version via

devtools::install_github('prestodb/RPresto')

Examples

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()

How RPresto works

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.

License

RPresto is BSD-licensed.

[1] See https://github.com/prestodb/presto/wiki/HTTP-Protocol for a description of the API.