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))
+  )
+})