Read and Write Parquet Files

Thin, dependency-light wrappers around DuckDB for reading tabular files into tibbles and for writing data frames as Parquet. These are the readers used throughout isoformic: annotation tables, experiment caches and the bundled example data are all stored as Parquet.

Usage

read_parquet(path, columns = NULL, n_max = Inf, ...)

read_tabular(path, columns = NULL, n_max = Inf, ...)

write_parquet(
  x,
  path,
  compression = c("zstd", "snappy", "gzip", "uncompressed"),
  ...
)

Arguments

path

Path to the file to read or write.

columns

Optional character vector of columns to read. NULL reads all columns.

n_max

Maximum number of rows to read. Inf (default) reads all.

...

Reserved for future use; must be empty.

x

A data frame (or tibble) to write.

compression

Parquet compression codec.

Value

read_parquet() and read_tabular() return a tibble. write_parquet() returns path, invisibly.

Details

read_parquet() reads a Parquet file. read_tabular() reads Parquet, CSV or TSV files (.csv, .tsv, .tab, .txt, Salmon .sf; optionally gzip-compressed), auto-detecting delimiter and types. write_parquet() writes any data frame to a Parquet file, creating parent directories as needed.

Factor columns are stored as Parquet strings and come back as character. Row names are not stored; keep identifiers in a regular column.

Examples

tmp <- tempfile(fileext = ".parquet")
write_parquet(data.frame(id = c("a", "b"), value = c(1.5, 2)), tmp)
read_parquet(tmp)
#> # A tibble: 2 × 2
#>   id    value
#>   <chr> <dbl>
#> 1 a       1.5
#> 2 b       2  
read_parquet(tmp, columns = "id", n_max = 1)
#> # A tibble: 1 × 1
#>   id   
#>   <chr>
#> 1 a    
read_tabular(tmp)
#> # A tibble: 2 × 2
#>   id    value
#>   <chr> <dbl>
#> 1 a       1.5
#> 2 b       2