Implement $struct$unnest()

NEWS.md

@@ -114,6 +114,7 @@
 - New methods `$select_seq()` and `$with_columns_seq()` for `DataFrame` and
  `LazyFrame` (#1003).
 - New method `$clear()` for `DataFrame`, `LazyFrame`, and `Series` (#1004).
+- New method `$struct$unnest()` for `Series` (#1010).
 
 ### Bug fixes
 

R/extendr-wrappers.R

@@ -1324,6 +1324,8 @@ RPolarsSeries$set_sorted_mut <- function(descending) invisible(.Call(wrap__RPola
 
 RPolarsSeries$struct_fields <- function() .Call(wrap__RPolarsSeries__struct_fields, self)
 
+RPolarsSeries$struct_unnest <- function() .Call(wrap__RPolarsSeries__struct_unnest, self)
+
 RPolarsSeries$from_arrow_array_stream_str <- function(name, robj_str) .Call(wrap__RPolarsSeries__from_arrow_array_stream_str, name, robj_str)
 
 RPolarsSeries$from_arrow_array_robj <- function(name, array) .Call(wrap__RPolarsSeries__from_arrow_array_robj, name, array)

R/series__series.R

@@ -270,7 +270,19 @@ Series_struct = method_as_active_binding(
  self, expr_struct_make_sub_ns,
  fields = method_as_active_binding(function() {
  unwrap(.pr$Series$struct_fields(pl_series), "in $struct$fields:")
- })
+ }),
+ #' Convert this struct Series to a DataFrame with a separate column for
+ #' each field
+ #'
+ #' @name Series_struct_unnest
+ #' @return A DataFrame
+ #' @examples
+ #' s = pl$Series(values = c(1, 2), dtype = pl$Struct(foo = pl$Float64))
+ #' s$struct$unnest()
+ unnest = function() {
+ .pr$Series$struct_unnest(pl_series) |>
+ unwrap("in $struct$unnest():")
+ }
  )
  }
 )
@@ -1101,8 +1113,6 @@ Series_item = function(index = NULL) {
 #'
 #' s$clear(n = 5)
 Series_clear = function(n = 0) {
- # TODO: check whether n < 0 should be removed when resolved upstream
- # https://github.com/pola-rs/polars/issues/15421
  if (length(n) > 1 || !is.numeric(n) || n < 0) {
  Err_plain("`n` must be an integer greater or equal to 0.") |>
  unwrap("in $clear():")

src/rust/src/series.rs

@@ -505,6 +505,12 @@ impl RPolarsSeries {
  Ok(ca.fields().iter().map(|s| s.name()).collect())
  }
 
+ fn struct_unnest(&self) -> RResult<RPolarsDataFrame> {
+ let ca = self.0.struct_().map_err(polars_to_rpolars_err)?;
+ let out: pl::DataFrame = ca.clone().into();
+ Ok(out.into())
+ }
+
  pub fn from_arrow_array_stream_str(name: Robj, robj_str: Robj) -> RResult<Robj> {
  let name = robj_to!(str, name)?;
  let s = crate::arrow_interop::to_rust::arrow_stream_to_series_internal(robj_str)?

tests/testthat/_snaps/after-wrappers.md

@@ -717,10 +717,11 @@
  [37] "rep" "set_sorted_mut" 
  [39] "shape" "sleep" 
  [41] "sort_mut" "std" 
- [43] "struct_fields" "sub" 
- [45] "sum" "to_fmt_char" 
- [47] "to_frame" "to_r" 
- [49] "value_counts" "var" 
+ [43] "struct_fields" "struct_unnest" 
+ [45] "sub" "sum" 
+ [47] "to_fmt_char" "to_frame" 
+ [49] "to_r" "value_counts" 
+ [51] "var" 
 
 # public and private methods of each class RThreadHandle
 

tests/testthat/test-series.R

@@ -679,3 +679,25 @@ test_that("$clear() works", {
  "greater or equal to 0"
  )
 })
+
+test_that("$struct$unnest() works", {
+ s = pl$Series(values = c(1, 2), dtype = pl$Struct(foo = pl$Float64))
+ expect_identical(
+ s$struct$unnest()$to_list(),
+ list(foo = c(1, 2))
+ )
+
+ # empty Series
+ s = pl$Series(dtype = pl$Struct(foo = pl$Float64))
+ expect_identical(
+ s$struct$unnest()$to_list(),
+ list(foo = numeric(0))
+ )
+
+ # Series "name" param is not used, only pl$Struct() name is used
+ s = pl$Series(name = "bar", dtype = pl$Struct(foo = pl$Float64))
+ expect_identical(
+ s$struct$unnest()$to_list(),
+ list(foo = numeric(0))
+ )
+})