Create a lazy table reference from a delimited text file

Opens a delimited text file (CSV, TSV, or any single-character separator) for lazy, streaming query execution. Column types are inferred from the first guess_max rows (default 1000). No data is read until collect() is called. Gzip-compressed files (.csv.gz, .tsv.gz) are supported transparently.

Usage

tbl_csv(
  path,
  batch_size = .DEFAULT_BATCH_SIZE,
  delim = ",",
  guess_max = 1000,
  col_types = NULL
)

Arguments

path

Path to a delimited text file, optionally gzip-compressed.

batch_size

Number of rows per batch (default 65536).

delim

Single-character field separator (default ","). Use "\t" for tab-separated and ";" for semicolon-separated files.

guess_max

Number of rows scanned to infer column types (default 1000). A value that only reveals a column's true type later in the file (for example an integer column that turns out to hold a decimal past row 1000) is otherwise read as NA; pass a larger value, or Inf to scan the whole file, at the cost of an extra read pass.

col_types

Optional named character vector forcing the type of specific columns, overriding inference. Names are column names; values are one of "character", "double", "integer", or "logical". Use this to keep a zero-padded identifier column (ZIP codes, accession IDs) as text instead of letting it be read as a number, e.g. col_types = c(zip = "character").

Value

A vectra_node object representing a lazy scan of the file.

Details

The field separator is set by delim, so tab-separated files (GBIF occurrence exports, TSV dumps) and semicolon-separated files (many European exports) are read natively without a transcode step. Quoting follows RFC 4180 for every delimiter: a field wrapped in double quotes may contain the delimiter, newlines, and doubled quotes.

Examples

f <- tempfile(fileext = ".csv")
write.csv(mtcars, f, row.names = FALSE)
node <- tbl_csv(f)
print(node)
unlink(f)

# Tab-separated (e.g. a GBIF occurrence export)
g <- tempfile(fileext = ".tsv")
write.table(mtcars, g, sep = "\t", row.names = FALSE, quote = FALSE)
tbl_csv(g, delim = "\t") |> collect() |> head()
unlink(g)