README

Building on data.frame serialization provided by fst, prt offers an interface for working with partitioned data.frames, saved as individual fst files.

Installation

source("https://install-github.me/nbenn/prt")

Alternatively, if you have the remotes package available, the latest release is available by calling install_github() as

# install.packages("remotes")
remotes::install_github("nbenn/prt@*release")

Short demo

Creating a prt object can be done either by calling new_prt() on a list of previously created fst files or by coercing a data.frame object to prt using as_prt().

tmp <- tempfile()
dir.create(tmp)

flights <- as_prt(nycflights13::flights, n_chunks = 2L, dir = tmp)
#> fstcore package v0.9.12
#> (OpenMP was not detected, using single threaded mode)

print(flights)
#> # A prt:        336,776 × 19
#> # Partitioning: [168,388, 168,388] rows
#>          year month   day dep_time sched_dep_time dep_delay arr_time
#>         <int> <int> <int>    <int>          <int>     <dbl>    <int>
#>       1  2013     1     1      517            515         2      830
#>       2  2013     1     1      533            529         4      850
#>       3  2013     1     1      542            540         2      923
#>       4  2013     1     1      544            545        -1     1004
#>       5  2013     1     1      554            600        -6      812
#>       …
#> 336,772  2013     9    30       NA           1455        NA       NA
#> 336,773  2013     9    30       NA           2200        NA       NA
#> 336,774  2013     9    30       NA           1210        NA       NA
#> 336,775  2013     9    30       NA           1159        NA       NA
#> 336,776  2013     9    30       NA            840        NA       NA
#> # … with 336,766 more rows, and 12 more variables: sched_arr_time <int>,
#> #   arr_delay <dbl>, carrier <chr>, flight <int>, tailnum <chr>, origin <chr>,
#> #   dest <chr>, air_time <dbl>, distance <dbl>, hour <dbl>, minute <dbl>,
#> #   time_hour <dttm>

In case a prt object is created from a data.frame, the specified number of files is written to the directory of choice (a newly created directory within tempdir() by default).

list.files(tmp)
#> [1] "1.fst" "2.fst"

Subsetting and printing is closely modeled after tibble and behavior that deviates from that of tibble will most likely be considered a bug (please report). Some design choices that do set a prt object apart from a tibble include the use of data.tables for any result of a subsetting operation and the complete disregard for row.names.

In addition to standard subsetting operations involving the functions `[`(), `[[`() and `$`(), the base generic function subset() is implemented for the prt class, enabling subsetting operations using non-standard evaluation. Combined with random access to tables stored as fst files, this can make data access more efficient in cases where only a subset of the data is of interest.

jan <- flights[flights$month == 1, ]
identical(jan, subset(flights, month == 1))
#> [1] TRUE
print(jan)
#>        year month day dep_time sched_dep_time dep_delay arr_time sched_arr_time
#>     1: 2013     1   1      517            515         2      830            819
#>     2: 2013     1   1      533            529         4      850            830
#>     3: 2013     1   1      542            540         2      923            850
#>     4: 2013     1   1      544            545        -1     1004           1022
#>     5: 2013     1   1      554            600        -6      812            837
#>    ---                                                                         
#> 27000: 2013     1  31       NA           1325        NA       NA           1505
#> 27001: 2013     1  31       NA           1200        NA       NA           1430
#> 27002: 2013     1  31       NA           1410        NA       NA           1555
#> 27003: 2013     1  31       NA           1446        NA       NA           1757
#> 27004: 2013     1  31       NA            625        NA       NA            934
#>        arr_delay carrier flight tailnum origin dest air_time distance hour
#>     1:        11      UA   1545  N14228    EWR  IAH      227     1400    5
#>     2:        20      UA   1714  N24211    LGA  IAH      227     1416    5
#>     3:        33      AA   1141  N619AA    JFK  MIA      160     1089    5
#>     4:       -18      B6    725  N804JB    JFK  BQN      183     1576    5
#>     5:       -25      DL    461  N668DN    LGA  ATL      116      762    6
#>    ---                                                                    
#> 27000:        NA      MQ   4475  N730MQ    LGA  RDU       NA      431   13
#> 27001:        NA      MQ   4658  N505MQ    LGA  ATL       NA      762   12
#> 27002:        NA      MQ   4491  N734MQ    LGA  CLE       NA      419   14
#> 27003:        NA      UA    337    <NA>    LGA  IAH       NA     1416   14
#> 27004:        NA      UA   1497    <NA>    LGA  IAH       NA     1416    6
#>        minute           time_hour
#>     1:     15 2013-01-01 05:00:00
#>     2:     29 2013-01-01 05:00:00
#>     3:     40 2013-01-01 05:00:00
#>     4:     45 2013-01-01 05:00:00
#>     5:      0 2013-01-01 06:00:00
#>    ---                           
#> 27000:     25 2013-01-31 13:00:00
#> 27001:      0 2013-01-31 12:00:00
#> 27002:     10 2013-01-31 14:00:00
#> 27003:     46 2013-01-31 14:00:00
#> 27004:     25 2013-01-31 06:00:00

A subsetting operation on a prt object yields a data.table. If the full table is of interest, a prt-specific implementation of the as.data.table() generic is available.