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Inner workings of the Series-class

Description

The Series-class is simply two environments of respectively the public and private methods/function calls to the polars rust side. The instantiated Series-object is an externalptr to a lowlevel rust polars Series object. The pointer address is the only statefullness of the Series object on the R side. Any other state resides on the rust side. The S3 method .DollarNames.RPolarsSeries exposes all public $foobar()-methods which are callable onto the object. Most methods return another Series-class instance or similar which allows for method chaining. This class system in lack of a better name could be called "environment classes" and is the same class system extendr provides, except here there is both a public and private set of methods. For implementation reasons, the private methods are external and must be called from .pr$Series$methodname(), also all private methods must take any self as an argument, thus they are pure functions. Having the private methods as pure functions solved/simplified self-referential complications.

Details

Check out the source code in R/Series_frame.R how public methods are derived from private methods. Check out extendr-wrappers.R to see the extendr-auto-generated methods. These are moved to .pr and converted into pure external functions in after-wrappers.R. In zzz.R (named zzz to be last file sourced) the extendr-methods are removed and replaced by any function prefixed Series_.

Active bindings

dtype

$dtype returns the data type of the Series.

flags

$flags returns a named list with flag names and their values.

Flags are used internally to avoid doing unnecessary computations, such as sorting a variable that we know is already sorted. The number of flags varies depending on the column type: columns of type array and list have the flags SORTED_ASC, SORTED_DESC, and FAST_EXPLODE, while other column types only have the former two.

  • SORTED_ASC is set to TRUE when we sort a column in increasing order, so that we can use this information later on to avoid re-sorting it.
  • SORTED_DESC is similar but applies to sort in decreasing order.

name

$name returns the name of the Series.

shape

$shape returns a numeric vector of length two with the number of length of the Series and width of the Series (always 1).

Expression methods

Series stores most of all Expr methods.

Some of these are stored in sub-namespaces.

arr

$arr stores all array related methods.

bin

$bin stores all binary related methods.

cat

$cat stores all categorical related methods.

dt

$dt stores all temporal related methods.

list

$list stores all list related methods.

str

$str stores all string related methods.

struct

$struct stores all struct related methods and active bindings.

Active bindings specific to Series:

  • $struct$fields: Returns a character vector of the fields in the struct.

Conversion to R data types considerations

When converting Polars objects, such as DataFrames to R objects, for example via the as.data.frame() generic function, each type in the Polars object is converted to an R type. In some cases, an error may occur because the conversion is not appropriate. In particular, there is a high possibility of an error when converting a Datetime type without a time zone. A Datetime type without a time zone in Polars is converted to the POSIXct type in R, which takes into account the time zone in which the R session is running (which can be checked with the Sys.timezone() function). In this case, if ambiguous times are included, a conversion error will occur. In such cases, change the session time zone using Sys.setenv(TZ = "UTC") and then perform the conversion, or use the $dt$replace_time_zone() method on the Datetime type column to explicitly specify the time zone before conversion.

# Due to daylight savings, clocks were turned forward 1 hour on Sunday, March 8, 2020, 2:00:00 am
# so this particular date-time doesn't exist
non_existent_time = as_polars_series("2020-03-08 02:00:00")\$str\$strptime(pl\$Datetime(), "%F %T")

withr::with_envvar(
  new = c(TZ = "America/New_York"),
  {
    tryCatch(
      # This causes an error due to the time zone (the `TZ` env var is affected).
      as.vector(non_existent_time),
      error = function(e) e
    )
  }
)
#> <error: in to_r: ComputeError(ErrString("datetime '2020-03-08 02:00:00' is non-existent in time zone 'America/New_York'. You may be able to use `non_existent='null'` to return `null` in this case.")) When calling: devtools::document()>

withr::with_envvar(
  new = c(TZ = "America/New_York"),
  {
    # This is safe.
    as.vector(non_existent_time\$dt\$replace_time_zone("UTC"))
  }
)
#> [1] "2020-03-08 02:00:00 UTC"

Examples

library(polars)

# make a Series
s = as_polars_series(c(1:3, 1L))

# call an active binding
s$shape
#> [1] 4 1
# show flags
s$sort()$flags
#> $SORTED_ASC
#> [1] TRUE
#> 
#> $SORTED_DESC
#> [1] FALSE
# use Expr method
s$cos()
#> polars Series: shape: (4,)
#> Series: '' [f64]
#> [
#>  0.540302
#>  -0.416147
#>  -0.989992
#>  0.540302
#> ]
# use Expr method in subnamespaces
as_polars_series(list(3:1, 1:2, NULL))$list$first()
#> polars Series: shape: (3,)
#> Series: '' [i32]
#> [
#>  3
#>  1
#>  null
#> ]
as_polars_series(c(1, NA, 2))$str$join("-")
#> polars Series: shape: (1,)
#> Series: '' [str]
#> [
#>  "1.0-2.0"
#> ]
s = pl$date_range(
  as.Date("2024-02-18"), as.Date("2024-02-24"),
  interval = "1d"
)$to_series()
s
#> polars Series: shape: (7,)
#> Series: '' [date]
#> [
#>  2024-02-18
#>  2024-02-19
#>  2024-02-20
#>  2024-02-21
#>  2024-02-22
#>  2024-02-23
#>  2024-02-24
#> ]
s$dt$day()
#> polars Series: shape: (7,)
#> Series: '' [i8]
#> [
#>  18
#>  19
#>  20
#>  21
#>  22
#>  23
#>  24
#> ]
# Other active bindings in subnamespaces
as_polars_series(data.frame(a = 1:2, b = 3:4))$struct$fields
#> [1] "a" "b"
# show all available methods for Series
pl$show_all_public_methods("RPolarsSeries")
#> 
#> 
#>     RPolarsSeries class methods, access via object$method() ( environment ):
#> 
#>        RPolarsSeries ( environment ):
#>           [ abs ; function ]
#>           [ add ; function ]
#>           [ alias ; function ]
#>           [ all ; function ]
#>           [ and ; function ]
#>           [ any ; function ]
#>           [ append ; function ]
#>           [ approx_n_unique ; function ]
#>           [ arccos ; function ]
#>           [ arccosh ; function ]
#>           [ arcsin ; function ]
#>           [ arcsinh ; function ]
#>           [ arctan ; function ]
#>           [ arctanh ; function ]
#>           [ arg_max ; function ]
#>           [ arg_min ; function ]
#>           [ arg_sort ; function ]
#>           [ arg_unique ; function ]
#>           [ arr ; property function ]
#>           [ backward_fill ; function ]
#>           [ bin ; property function ]
#>           [ bottom_k ; function ]
#>           [ cast ; function ]
#>           [ cat ; property function ]
#>           [ ceil ; function ]
#>           [ chunk_lengths ; function ]
#>           [ clear ; function ]
#>           [ clip ; function ]
#>           [ clip_max ; function ]
#>           [ clip_min ; function ]
#>           [ clone ; function ]
#>           [ compare ; function ]
#>           [ cos ; function ]
#>           [ cosh ; function ]
#>           [ count ; function ]
#>           [ cum_count ; function ]
#>           [ cum_max ; function ]
#>           [ cum_min ; function ]
#>           [ cum_prod ; function ]
#>           [ cum_sum ; function ]
#>           [ cumulative_eval ; function ]
#>           [ cut ; function ]
#>           [ diff ; function ]
#>           [ div ; function ]
#>           [ dot ; function ]
#>           [ drop_nans ; function ]
#>           [ drop_nulls ; function ]
#>           [ dt ; property function ]
#>           [ dtype ; property function ]
#>           [ entropy ; function ]
#>           [ eq ; function ]
#>           [ eq_missing ; function ]
#>           [ equals ; function ]
#>           [ ewm_mean ; function ]
#>           [ ewm_std ; function ]
#>           [ ewm_var ; function ]
#>           [ exp ; function ]
#>           [ explode ; function ]
#>           [ extend_constant ; function ]
#>           [ fill_nan ; function ]
#>           [ fill_null ; function ]
#>           [ filter ; function ]
#>           [ first ; function ]
#>           [ flags ; property function ]
#>           [ flatten ; function ]
#>           [ floor ; function ]
#>           [ floor_div ; function ]
#>           [ forward_fill ; function ]
#>           [ gather ; function ]
#>           [ gather_every ; function ]
#>           [ gt ; function ]
#>           [ gt_eq ; function ]
#>           [ has_nulls ; function ]
#>           [ hash ; function ]
#>           [ head ; function ]
#>           [ implode ; function ]
#>           [ interpolate ; function ]
#>           [ is_between ; function ]
#>           [ is_duplicated ; function ]
#>           [ is_finite ; function ]
#>           [ is_first_distinct ; function ]
#>           [ is_in ; function ]
#>           [ is_infinite ; function ]
#>           [ is_last_distinct ; function ]
#>           [ is_nan ; function ]
#>           [ is_not_nan ; function ]
#>           [ is_not_null ; function ]
#>           [ is_null ; function ]
#>           [ is_numeric ; function ]
#>           [ is_sorted ; function ]
#>           [ is_unique ; function ]
#>           [ item ; function ]
#>           [ kurtosis ; function ]
#>           [ last ; function ]
#>           [ len ; function ]
#>           [ limit ; function ]
#>           [ list ; property function ]
#>           [ log ; function ]
#>           [ log10 ; function ]
#>           [ lower_bound ; function ]
#>           [ lt ; function ]
#>           [ lt_eq ; function ]
#>           [ map_batches ; function ]
#>           [ map_elements ; function ]
#>           [ max ; function ]
#>           [ mean ; function ]
#>           [ median ; function ]
#>           [ min ; function ]
#>           [ mod ; function ]
#>           [ mode ; function ]
#>           [ mul ; function ]
#>           [ n_chunks ; function ]
#>           [ n_unique ; function ]
#>           [ name ; property function ]
#>           [ nan_max ; function ]
#>           [ nan_min ; function ]
#>           [ neq ; function ]
#>           [ neq_missing ; function ]
#>           [ not ; function ]
#>           [ null_count ; function ]
#>           [ or ; function ]
#>           [ pct_change ; function ]
#>           [ peak_max ; function ]
#>           [ peak_min ; function ]
#>           [ pow ; function ]
#>           [ print ; function ]
#>           [ product ; function ]
#>           [ qcut ; function ]
#>           [ quantile ; function ]
#>           [ rank ; function ]
#>           [ rechunk ; function ]
#>           [ reinterpret ; function ]
#>           [ rename ; function ]
#>           [ rep ; function ]
#>           [ repeat_by ; function ]
#>           [ replace ; function ]
#>           [ replace_strict ; function ]
#>           [ reshape ; function ]
#>           [ reverse ; function ]
#>           [ rle ; function ]
#>           [ rle_id ; function ]
#>           [ rolling_max ; function ]
#>           [ rolling_max_by ; function ]
#>           [ rolling_mean ; function ]
#>           [ rolling_mean_by ; function ]
#>           [ rolling_median ; function ]
#>           [ rolling_median_by ; function ]
#>           [ rolling_min ; function ]
#>           [ rolling_min_by ; function ]
#>           [ rolling_quantile ; function ]
#>           [ rolling_quantile_by ; function ]
#>           [ rolling_skew ; function ]
#>           [ rolling_std ; function ]
#>           [ rolling_std_by ; function ]
#>           [ rolling_sum ; function ]
#>           [ rolling_sum_by ; function ]
#>           [ rolling_var ; function ]
#>           [ rolling_var_by ; function ]
#>           [ round ; function ]
#>           [ sample ; function ]
#>           [ search_sorted ; function ]
#>           [ set_sorted ; function ]
#>           [ shape ; property function ]
#>           [ shift ; function ]
#>           [ shift_and_fill ; function ]
#>           [ shrink_dtype ; function ]
#>           [ shuffle ; function ]
#>           [ sign ; function ]
#>           [ sin ; function ]
#>           [ sinh ; function ]
#>           [ skew ; function ]
#>           [ slice ; function ]
#>           [ sort ; function ]
#>           [ sort_by ; function ]
#>           [ sqrt ; function ]
#>           [ std ; function ]
#>           [ str ; property function ]
#>           [ struct ; property function ]
#>           [ sub ; function ]
#>           [ sum ; function ]
#>           [ tail ; function ]
#>           [ tan ; function ]
#>           [ tanh ; function ]
#>           [ to_frame ; function ]
#>           [ to_list ; function ]
#>           [ to_lit ; function ]
#>           [ to_physical ; function ]
#>           [ to_r ; function ]
#>           [ to_vector ; function ]
#>           [ top_k ; function ]
#>           [ unique ; function ]
#>           [ unique_counts ; function ]
#>           [ upper_bound ; function ]
#>           [ value_counts ; function ]
#>           [ var ; function ]
#>           [ xor ; function ]