Performance notes
In datasusr: Fast Access to Brazilian Public Health Data from 'DATASUS'

knitr::opts_chunk$set(collapse = TRUE, comment = "#>")

This vignette collects practical advice for reading large DATASUS files efficiently with datasusr.

Column selection

The single most effective way to speed up reads is to select only the columns you need. The C parser skips over unneeded fields at the byte level, so fewer columns means less allocation and less parsing:

library(datasusr)

# Slow: reads all ~100+ columns
x <- read_datasus_dbc("RDPE2401.dbc")

# Fast: reads only 4 columns
x <- read_datasus_dbc(
  "RDPE2401.dbc",
  select = c("uf_zi", "ano_cmpt", "munic_res", "val_tot")
)

Type inference

When guess_types = TRUE (the default), the reader scans every value of each numeric field to decide whether it fits in an integer or requires a double. Disabling this skips the scan and relies on the DBF field metadata alone:

x <- read_datasus_dbc("RDPE2401.dbc", guess_types = FALSE)

This is safe for most analyses and can save noticeable time on files with millions of rows.

Explicit types

When you know exactly which types you need, col_types lets you specify them upfront and skip inference entirely:

x <- read_datasus_dbc(
  "RDPE2401.dbc",
  select      = c("uf_zi", "dt_inter", "val_tot"),
  col_types   = c(uf_zi = "character", dt_inter = "date", val_tot = "double"),
  parse_dates = TRUE,
  guess_types = FALSE
)

Date parsing

Date parsing (parse_dates = TRUE) adds a small overhead per date field. Only enable it when you actually need Date objects; otherwise the raw YYYYMMDD character strings are often sufficient for filtering and grouping.

Benchmarking example

library(bench)

file <- "RDPE2401.dbc"

bench::mark(
  default    = read_datasus_dbc(file),
  no_guess   = read_datasus_dbc(file, guess_types = FALSE),
  selected   = read_datasus_dbc(file, select = c("uf_zi", "val_tot")),
  typed      = read_datasus_dbc(
    file,
    select      = c("uf_zi", "dt_inter", "val_tot"),
    col_types   = c(uf_zi = "character", dt_inter = "date", val_tot = "double"),
    parse_dates = TRUE,
    guess_types = FALSE
  ),
  check      = FALSE,
  iterations = 5
)

Memory

datasusr allocates R vectors directly from C without materialising intermediate files on disk. For very large datasets (tens of millions of rows), consider processing files in batches rather than binding everything into a single data frame.