Appendix A — Arrow, Parquet and DuckDB

B Arrow, Parquet and DuckDB

B.1 Introduction

Everything so far fit in memory as CSV. Two tools cover the next scale, and both speak the dplyr you already know:

• Parquet (via arrow) — a compressed columnar file format. The same data takes far less disk and reads much faster than CSV.
• DuckDB (via duckplyr) — an in-process analytical database. dplyr verbs run inside it, so data larger than memory stays on disk until collect().

Both are optional: install them with install.packages(c("arrow", "duckdb", "duckplyr")). The chunks below run only when the packages are present (eval = requireNamespace(...)), so the book still builds without them. Browser execution of parquet is intentionally deferred until WebR binary sizes are checked (see the P2 plan).

B.2 Parquet with arrow

Write ecom to parquet and read it back. The round-trip lands in a temporary directory, so nothing litters the project:

library(dplyr)
library(readr)
library(arrow)

ecom <-
  read_csv('https://raw.githubusercontent.com/rsquaredacademy/datasets/master/web.csv',
    col_types = cols_only(device = col_factor(levels = c("laptop", "tablet", "mobile")),
      referrer = col_factor(levels = c("bing", "direct", "social", "yahoo", "google")),
      purchase = col_logical(), n_pages = col_double(), n_visit = col_double(),
      duration = col_double(), order_value = col_double(), order_items = col_double()
    )
  )

pq <- file.path(tempdir(), "ecom.parquet")
cs <- file.path(tempdir(), "ecom.csv")
write_parquet(ecom, pq)
write_csv(ecom, cs)

# same rows, roughly half the bytes
c(csv_bytes = file.size(cs), parquet_bytes = file.size(pq))

    csv_bytes parquet_bytes 
        32287         14878 

read_parquet() returns a tibble, so every verb from @dplyr-basics works unchanged:

ecom_pq <- read_parquet(pq)
class(ecom_pq)

[1] "spec_tbl_df" "tbl_df"      "tbl"         "data.frame" 

ecom_pq |>
  filter(purchase) |>
  summarise(revenue = sum(order_value), orders = n(), .by = device)

# A tibble: 3 × 3
  device revenue orders
  <fct>    <dbl>  <int>
1 tablet   51321     36
2 mobile   51504     36
3 laptop   56531     31

B.3 DuckDB with duckplyr

duckdb_tibble() (duckplyr >= 1.0) moves a data frame into DuckDB and hands back a lazy table: dplyr verbs build the query, nothing runs until collect():

library(duckplyr)

ecom_duck <- duckdb_tibble(ecom)
class(ecom_duck)

[1] "duckplyr_df" "tbl_df"      "tbl"         "data.frame" 

ecom_duck |>
  filter(purchase) |>
  summarise(revenue = sum(order_value), orders = n(), .by = device) |>
  mutate(aov = revenue / orders) |>
  collect()

# A tibble: 3 × 4
  device revenue orders   aov
* <fct>    <dbl>  <int> <dbl>
1 laptop   56531     31 1824.
2 tablet   51321     36 1426.
3 mobile   51504     36 1431.

The numbers match the Chapter @dplyr-basics AOV exactly — the engine changed, the answers did not. Reach for this pattern when a single CSV no longer fits comfortably in memory: keep the data in DuckDB (or parquet on disk), push the verbs down, and collect() only the summary.