Read and write fst files

Wrapper for read_fst and write_fst from fst, but use a different default. For data import, always return a data.table. For data export, always compress the data to the smallest size.

export_fst(x, path, compress = 100, uniform_encoding = TRUE)

import_fst(
  path,
  columns = NULL,
  from = 1,
  to = NULL,
  as.data.table = TRUE,
  old_format = FALSE
)

Arguments

x	a data frame to write to disk
path	path to fst file
compress	value in the range 0 to 100, indicating the amount of compression to use. Lower values mean larger file sizes. The default compression is set to 50.
uniform_encoding	If `TRUE`, all character vectors will be assumed to have elements with equal encoding. The encoding (latin1, UTF8 or native) of the first non-NA element will used as encoding for the whole column. This will be a correct assumption for most use cases. If `uniform.encoding` is set to `FALSE`, no such assumption will be made and all elements will be converted to the same encoding. The latter is a relatively expensive operation and will reduce write performance for character columns.
columns	Column names to read. The default is to read all columns.
from	Read data starting from this row number.
to	Read data up until this row number. The default is to read to the last row of the stored dataset.
as.data.table	If TRUE, the result will be returned as a data.table object. Any keys set on dataset x before writing will be retained. This allows for storage of sorted datasets. This option requires data.table package to be installed.
old_format	must be FALSE, the old fst file format is deprecated and can only be read and converted with fst package versions 0.8.0 to 0.8.10.

Value

`import_fst` returns a data.table with the selected columns and rows. `export_fst` writes `x` to a `fst` file and invisibly returns `x` (so you can use this function in a pipeline).

See also

read_fst

Examples

# \donttest{
export_fst(iris,"iris_fst_test.fst")
iris_dt = import_fst("iris_fst_test.fst")
iris_dt
#>      Sepal.Length Sepal.Width Petal.Length Petal.Width   Species
#>   1:          5.1         3.5          1.4         0.2    setosa
#>   2:          4.9         3.0          1.4         0.2    setosa
#>   3:          4.7         3.2          1.3         0.2    setosa
#>   4:          4.6         3.1          1.5         0.2    setosa
#>   5:          5.0         3.6          1.4         0.2    setosa
#>  ---                                                            
#> 146:          6.7         3.0          5.2         2.3 virginica
#> 147:          6.3         2.5          5.0         1.9 virginica
#> 148:          6.5         3.0          5.2         2.0 virginica
#> 149:          6.2         3.4          5.4         2.3 virginica
#> 150:          5.9         3.0          5.1         1.8 virginica
unlink("iris_fst_test.fst")
# }