Read and write data frames from and to a fast-storage (fst) file. Allows for compression and (file level) random access of stored data, even for compressed datasets. When using a data.table object for x, the key (if any) is preserved, allowing storage of sorted data. Methods read_fst and write_fst are equivalent to read.fst and write.fst (but the former syntax is preferred).

write_fst(x, path, compress = 50, uniform_encoding = TRUE)

read_fst(path, columns = NULL, from = 1, to = NULL, = FALSE, old_format = FALSE)

write.fst(x, path, compress = 50, uniform_encoding = TRUE)

read.fst(path, columns = NULL, from = 1, to = NULL, = FALSE, old_format = FALSE)



a data frame to write to disk


path to fst file


value in the range 0 to 100, indicating the amount of compression to use. Lower values mean larger file sizes.


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.


Column names to read. The default is to read all all columns.


Read data starting from this row number.


Read data up until this row number. The default is to read to the last row of the stored dataset.

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.


use TRUE to read fst files generated with a fst package version lower than v0.8.0


read_fst returns a data frame with the selected columns and rows. read_fst invisibly returns x (so you can use this function in a pipeline).


# Sample dataset x <- data.frame(A = 1:10000, B = sample(c(TRUE, FALSE, NA), 10000, replace = TRUE)) # Uncompressed write_fst(x, "dataset.fst") # filesize: 41 KB y <- read_fst("dataset.fst") # read uncompressed data # Compressed write_fst(x, "dataset.fst", 100) # fileSize: 4 KB y <- read_fst("dataset.fst") # read compressed data # Random access y <- read_fst("dataset.fst", "B") # read selection of columns y <- read_fst("dataset.fst", "A", 100, 200) # read selection of columns and rows