Implements Series.split_into/3

lib/explorer/backend/lazy_series.ex

@@ -127,6 +127,7 @@ defmodule Explorer.Backend.LazySeries do
     downcase: 1,
     substring: 3,
     split: 2,
+    split_into: 3,
     json_decode: 2,
     json_path_match: 2,
     # Float round
@@ -1053,6 +1054,13 @@ defmodule Explorer.Backend.LazySeries do
     Backend.Series.new(data, {:list, :string})
   end
 
+  @impl true
+  def split_into(series, by, fields) do
+    data = new(:split_into, [lazy_series!(series), by, fields], :string)
+
+    Backend.Series.new(data, {:struct, Enum.map(fields, &{&1, :string})})
+  end
+
   @impl true
   def round(series, decimals) when is_integer(decimals) and decimals >= 0 do
     data = new(:round, [lazy_series!(series), decimals], {:f, 64})

lib/explorer/backend/series.ex

@@ -287,6 +287,7 @@ defmodule Explorer.Backend.Series do
   @callback rstrip(s, String.t() | nil) :: s
   @callback substring(s, integer(), non_neg_integer() | nil) :: s
   @callback split(s, String.t()) :: s
+  @callback split_into(s, String.t(), list(String.t() | atom())) :: s
   @callback json_decode(s, dtype()) :: s
   @callback json_path_match(s, String.t()) :: s
 

lib/explorer/polars_backend/expression.ex

@@ -136,6 +136,7 @@ defmodule Explorer.PolarsBackend.Expression do
     upcase: 1,
     substring: 3,
     split: 2,
+    split_into: 3,
     json_decode: 2,
     json_path_match: 2,
 

lib/explorer/polars_backend/native.ex

@@ -413,6 +413,7 @@ defmodule Explorer.PolarsBackend.Native do
   def s_cut(_s, _bins, _labels, _break_point_label, _category_label), do: err()
   def s_substring(_s, _offset, _length), do: err()
   def s_split(_s, _by), do: err()
+  def s_split_into(_s, _by, _num_fields), do: err()
 
   def s_qcut(_s, _quantiles, _labels, _break_point_label, _category_label),
     do: err()

lib/explorer/polars_backend/series.ex

@@ -694,6 +694,10 @@ defmodule Explorer.PolarsBackend.Series do
   def split(series, by),
     do: Shared.apply_series(series, :s_split, [by])
 
+  @impl true
+  def split_into(series, by, fields),
+    do: Shared.apply_series(series, :s_split_into, [by, fields])
+
   # Float round
   @impl true
   def round(series, decimals),

lib/explorer/series.ex

@@ -5651,6 +5651,32 @@ defmodule Explorer.Series do
   def split(%Series{dtype: dtype}, _by),
     do: dtype_error("split/2", dtype, [:string])
 
+  @doc """
+  Split a string Series into a struct of string `fields`.
+
+  The length of the field names list determines how many times the
+  string will be split at most. If the string cannot be split into that
+  many separate strings, null values will be provided for the
+  remaining fields.
+
+  ## Examples
+
+      iex> s = Series.from_list(["Smith, John", "Jones, Jane"])
+      iex> Series.split_into(s, ", ", ["Last Name", "First Name"])
+      #Explorer.Series<
+        Polars[2]
+        struct[2] [%{"First Name" => "John", "Last Name" => "Smith"}, %{"First Name" => "Jane", "Last Name" => "Jones"}]
+      >
+
+  """
+  @doc type: :string_wise
+  @spec split_into(Series.t(), String.t(), list(String.t() | atom())) :: Series.t()
+  def split_into(%Series{dtype: :string} = series, by, [_ | _] = fields) when is_binary(by),
+    do: apply_series(series, :split_into, [by, Enum.map(fields, &to_string/1)])
+
+  def split_into(%Series{dtype: dtype}, by, [_ | _]) when is_binary(by),
+    do: dtype_error("split_into/3", dtype, [:string])
+
   # Float
 
   @doc """

native/explorer/src/expressions.rs

@@ -1115,6 +1115,18 @@ pub fn expr_json_path_match(expr: ExExpr, json_path: &str) -> ExExpr {
     ExExpr::new(expr)
 }
 
+#[rustler::nif]
+pub fn expr_split_into(expr: ExExpr, by: String, names: Vec<String>) -> ExExpr {
+    let expr = expr
+        .clone_inner()
+        .str()
+        .splitn(by.lit(), names.len())
+        .struct_()
+        .rename_fields(names);
+
+    ExExpr::new(expr)
+}
+
 #[rustler::nif]
 pub fn expr_struct(ex_exprs: Vec<ExExpr>) -> ExExpr {
     let exprs = ex_exprs.iter().map(|e| e.clone_inner()).collect();

native/explorer/src/lib.rs

@@ -273,6 +273,7 @@ rustler::init!(
         expr_substring,
         expr_replace,
         expr_json_path_match,
+        expr_split_into,
         // float round expressions
         expr_round,
         expr_floor,
@@ -456,6 +457,7 @@ rustler::init!(
         s_strip,
         s_substring,
         s_split,
+        s_split_into,
         s_subtract,
         s_sum,
         s_tail,

native/explorer/src/series.rs

@@ -1567,6 +1567,25 @@ pub fn s_split(s1: ExSeries, by: &str) -> Result<ExSeries, ExplorerError> {
     Ok(ExSeries::new(s2))
 }
 
+#[rustler::nif(schedule = "DirtyCpu")]
+pub fn s_split_into(s1: ExSeries, by: &str, names: Vec<String>) -> Result<ExSeries, ExplorerError> {
+    let s2 = s1
+        .clone_inner()
+        .into_frame()
+        .lazy()
+        .select([col(s1.name())
+            .str()
+            .splitn(by.lit(), names.len())
+            .struct_()
+            .rename_fields(names)
+            .alias(s1.name())])
+        .collect()?
+        .column(s1.name())?
+        .clone();
+
+    Ok(ExSeries::new(s2))
+}
+
 #[rustler::nif(schedule = "DirtyCpu")]
 pub fn s_round(s: ExSeries, decimals: u32) -> Result<ExSeries, ExplorerError> {
     Ok(ExSeries::new(s.round(decimals)?.into_series()))

test/explorer/data_frame_test.exs

@@ -1982,6 +1982,27 @@ defmodule Explorer.DataFrameTest do
                member?: [true, false]
              }
     end
+
+    test "splits a string column into multiple new columns" do
+      new_column_names = ["Last Name", "First Name"]
+      df = DF.new(%{names: ["Smith, John", "Jones, Jane"]})
+
+      df =
+        DF.mutate_with(df, fn ldf ->
+          %{names: Series.split_into(ldf[:names], ", ", new_column_names)}
+        end)
+        |> DF.unnest(:names)
+
+      assert DF.dtypes(df) == %{
+               "Last Name" => :string,
+               "First Name" => :string
+             }
+
+      assert DF.to_columns(df) == %{
+               "Last Name" => ["Smith", "Jones"],
+               "First Name" => ["John", "Jane"]
+             }
+    end
   end
 
   describe "sort_by/3" do
@@ -2618,17 +2639,13 @@ defmodule Explorer.DataFrameTest do
     end
 
     test "mixing nulls, signed, unsigned integers, and floats" do
-      df1 =
-        DF.new(x: Series.from_list([1, 2], dtype: :u16), y: Series.from_list(["a", "b"]))
+      df1 = DF.new(x: Series.from_list([1, 2], dtype: :u16), y: Series.from_list(["a", "b"]))
 
-      df2 =
-        DF.new(x: Series.from_list([3.0, 4.0], dtype: :f32), y: Series.from_list(["c", "d"]))
+      df2 = DF.new(x: Series.from_list([3.0, 4.0], dtype: :f32), y: Series.from_list(["c", "d"]))
 
-      df3 =
-        DF.new(x: [nil, nil], y: [nil, nil])
+      df3 = DF.new(x: [nil, nil], y: [nil, nil])
 
-      df4 =
-        DF.new(x: Series.from_list([5, 6], dtype: :s16), y: Series.from_list(["e", "f"]))
+      df4 = DF.new(x: Series.from_list([5, 6], dtype: :s16), y: Series.from_list(["e", "f"]))
 
       df5 = DF.concat_rows([df1, df2, df3, df4])
 

test/explorer/series_test.exs

@@ -5320,6 +5320,28 @@ defmodule Explorer.SeriesTest do
     end
   end
 
+  describe "split_into" do
+    test "split_into/3 produces the correct number of fields in a struct" do
+      series = Series.from_list(["Smith, John", "Jones, Jane"])
+      split_series = series |> Series.split_into(", ", ["Last Name", "First Name"])
+
+      assert Series.to_list(split_series) == [
+               %{"First Name" => "John", "Last Name" => "Smith"},
+               %{"First Name" => "Jane", "Last Name" => "Jones"}
+             ]
+    end
+
+    test "split_into/3 produces a nil field when string cannot be split for every field" do
+      series = Series.from_list(["Smith-John", "Jones-Jane"])
+      split_series = series |> Series.split_into("-", ["Last Name", "First Name", "Middle Name"])
+
+      assert Series.to_list(split_series) == [
+               %{"First Name" => "John", "Last Name" => "Smith", "Middle Name" => nil},
+               %{"First Name" => "Jane", "Last Name" => "Jones", "Middle Name" => nil}
+             ]
+    end
+  end
+
   describe "strptime/2 and strftime/2" do
     test "parse datetime from string" do
       series = Series.from_list(["2023-01-05 12:34:56", "XYZ", nil])