inst/doc/extend.R

In duckplyr: A 'DuckDB'-Backed Version of 'dplyr'

## ----include = FALSE----------------------------------------------------------
clean_output <- function(x, options) {
  x <- gsub("0x[0-9a-f]+", "0xdeadbeef", x)
  x <- gsub("dataframe_[0-9]*_[0-9]*", "      dataframe_42_42      ", x)
  x <- gsub("[0-9]*\\.___row_number ASC", "42.___row_number ASC", x)
  x <- gsub("─", "-", x)
  x
}

local({
  hook_source <- knitr::knit_hooks$get("document")
  knitr::knit_hooks$set(document = clean_output)
})

knitr::opts_chunk$set(
  collapse = TRUE,
  eval = identical(Sys.getenv("IN_PKGDOWN"), "true") || (getRversion() >= "4.1" && rlang::is_installed(c("conflicted", "nycflights13"))),
  comment = "#>"
)

Sys.setenv(DUCKPLYR_FALLBACK_COLLECT = 0)

## ----attach-------------------------------------------------------------------
# library(conflicted)
# library(dplyr)
# conflict_prefer("filter", "dplyr")

## ----extensibility------------------------------------------------------------
# library(conflicted)
# library(dplyr)
# conflict_prefer("filter", "dplyr")
# library(duckplyr)

## ----overwrite, echo = FALSE--------------------------------------------------
# methods_overwrite()

## ----extensibility2-----------------------------------------------------------
# # Create a relational to be used by examples below
# new_dfrel <- function(x) {
#   stopifnot(is.data.frame(x))
#   new_relational(list(x), class = "dfrel")
# }
# mtcars_rel <- new_dfrel(mtcars[1:5, 1:4])
# 
# # Example 1: return a data.frame
# rel_to_df.dfrel <- function(rel, ...) {
#   unclass(rel)[[1]]
# }
# rel_to_df(mtcars_rel)
# 
# # Example 2: A (random) filter
# rel_filter.dfrel <- function(rel, exprs, ...) {
#   df <- unclass(rel)[[1]]
# 
#   # A real implementation would evaluate the predicates defined
#   # by the exprs argument
#   new_dfrel(df[sample.int(nrow(df), 3, replace = TRUE), ])
# }
# 
# rel_filter(
#   mtcars_rel,
#   list(
#     relexpr_function(
#       "gt",
#       list(relexpr_reference("cyl"), relexpr_constant("6"))
#     )
#   )
# )
# 
# # Example 3: A custom projection
# rel_project.dfrel <- function(rel, exprs, ...) {
#   df <- unclass(rel)[[1]]
# 
#   # A real implementation would evaluate the expressions defined
#   # by the exprs argument
#   new_dfrel(df[seq_len(min(3, base::ncol(df)))])
# }
# 
# rel_project(
#   mtcars_rel,
#   list(relexpr_reference("cyl"), relexpr_reference("disp"))
# )
# 
# # Example 4: A custom ordering (eg, ascending by mpg)
# rel_order.dfrel <- function(rel, exprs, ...) {
#   df <- unclass(rel)[[1]]
# 
#   # A real implementation would evaluate the expressions defined
#   # by the exprs argument
#   new_dfrel(df[order(df[[1]]), ])
# }
# 
# rel_order(
#   mtcars_rel,
#   list(relexpr_reference("mpg"))
# )
# 
# # Example 5: A custom join
# rel_join.dfrel <- function(left, right, conds, join, ...) {
#   left_df <- unclass(left)[[1]]
#   right_df <- unclass(right)[[1]]
# 
#   # A real implementation would evaluate the expressions
#   # defined by the conds argument,
#   # use different join types based on the join argument,
#   # and implement the join itself instead of relaying to left_join().
#   new_dfrel(dplyr::left_join(left_df, right_df))
# }
# 
# rel_join(new_dfrel(data.frame(mpg = 21)), mtcars_rel)
# 
# # Example 6: Limit the maximum rows returned
# rel_limit.dfrel <- function(rel, n, ...) {
#   df <- unclass(rel)[[1]]
# 
#   new_dfrel(df[seq_len(n), ])
# }
# 
# rel_limit(mtcars_rel, 3)
# 
# # Example 7: Suppress duplicate rows
# #  (ignoring row names)
# rel_distinct.dfrel <- function(rel, ...) {
#   df <- unclass(rel)[[1]]
# 
#   new_dfrel(df[!duplicated(df), ])
# }
# 
# rel_distinct(new_dfrel(mtcars[1:3, 1:4]))
# 
# # Example 8: Return column names
# rel_names.dfrel <- function(rel, ...) {
#   df <- unclass(rel)[[1]]
# 
#   names(df)
# }
# 
# rel_names(mtcars_rel)