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).

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
#>             <num>       <num>        <num>       <num>    <fctr>
#>   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")
# }

Arguments

Value

See also

Examples