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https://issues.apache.org/jira/browse/ARROW-12688?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17381539#comment-17381539
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Neal Richardson commented on ARROW-12688:
-----------------------------------------
Building from the code at
https://github.com/pdet/duckdb-benchmark/blob/master/arrow/group_by_with_duckdb.R,
I've worked up a slightly different interface, something we could add to the
arrow package (adding duckdb and DBI to Suggests):
{code}
summarise.arrow_dplyr_query <- function(.data, ..., engine = c("arrow",
"duckdb")) {
if (match.arg(engine) == "duckdb") {
summarize_duck(.data, ...)
} else {
# Continue with the current contents of summarise.arrow_dplyr_query
# ...
}
}
summarise_duck <- function(.data, ...) {
# TODO better translation of aggregate functions, parse tree traversal
aggregates <- vapply(enquos(...), rlang::quo_name, "character")
tbl_name <- paste0(replicate(10, sample(LETTERS, 1, TRUE)), collapse = "")
con <- arrow_duck_connection()
duckdb::duckdb_register_arrow(con, tbl_name, .data$data)
on.exit(duckdb::duckdb_unregister_arrow(con, tbl_name))
groups_str <- paste(.data$groups, collapse = ", ")
aggr_str <- paste(aggregates, collapse = ", ")
# TODO use relational API instead of SQL string construction
DBI::dbGetQuery(con, sprintf("SELECT %s, %s FROM %s GROUP BY %s",
groups_str, aggr_str, tbl_name, groups_str ))
}
arrow_duck_connection <- function() {
con <- getOption("arrow_duck_con")
if (is.null(con)) {
con <- dbConnect(duckdb::duckdb())
# Use the same CPU count that the arrow library is set to
DBI::dbExecute(con, paste0("PRAGMA threads=", cpu_count()))
options(arrow_duck_con = con)
}
con
}
{code}
Thoughts?
> [R] Use DuckDB to query an Arrow Dataset
> ----------------------------------------
>
> Key: ARROW-12688
> URL: https://issues.apache.org/jira/browse/ARROW-12688
> Project: Apache Arrow
> Issue Type: New Feature
> Components: C++, R
> Reporter: Neal Richardson
> Assignee: Jonathan Keane
> Priority: Major
>
> DuckDB can read data from an Arrow C-interface stream. Once we can provide
> that struct from R, presumably DuckDB could query on that stream.
> A first step is just connecting the pieces. A second step would be to handle
> parts of the DuckDB query and push down filtering/projection to Arrow.
> We need a function something like this:
> {code}
> #' Run a DuckDB query on Arrow data
> #'
> #' @param .data An `arrow` data object: `Dataset`, `Table`, `RecordBatch`, or
> #' an `arrow_dplyr_query` containing filter/mutate/etc. expressions
> #' @return A `duckdb::duckdb_connection`
> to_duckdb <- function(.data) {
> # ARROW-12687: [C++][Python][Dataset] Convert Scanner into a
> RecordBatchReader
> reader <- Scanner$create(.data)$ToRecordBatchReader()
> # ARROW-12689: [R] Implement ArrowArrayStream C interface
> stream_ptr <- allocate_arrow_array_stream()
> on.exit(delete_arrow_array_stream(stream_ptr))
> ExportRecordBatchReader(x, stream_ptr)
> # TODO: DuckDB method to create table/connection from ArrowArrayStream ptr
> duckdb::duck_connection_from_arrow_stream(stream_ptr)
> }
> {code}
> Assuming this existed, we could do something like (a variation of
> https://arrow.apache.org/docs/r/articles/dataset.html):
> {code}
> ds <- open_dataset("nyc-taxi", partitioning = c("year", "month"))
> ds %>%
> filter(total_amount > 100, year == 2015) %>%
> select(tip_amount, total_amount, passenger_count) %>%
> mutate(tip_pct = 100 * tip_amount / total_amount) %>%
> to_duckdb() %>%
> group_by(passenger_count) %>%
> summarise(
> median_tip_pct = median(tip_pct),
> n = n()
> )
> {code}
> and duckdb would do the aggregation while the data reading, predicate
> pushdown, filtering, and projection would happen in Arrow. Or you could do
> {{dbGetQuery(ds, "SOME SQL")}} and that would evaluate on arrow data.
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