Add native expression for Series.split/2 (#875)

native/explorer/src/expressions.rs

@@ -887,6 +887,12 @@ pub fn expr_substring(expr: ExExpr, offset: i64, length: Option<u64>) -> ExExpr
     ExExpr::new(expr.str().slice(offset.lit(), length))
 }
 
+#[rustler::nif]
+pub fn expr_split(expr: ExExpr, substring: String) -> ExExpr {
+    let expr = expr.clone_inner();
+    ExExpr::new(expr.str().split(substring.lit()))
+}
+
 #[rustler::nif]
 pub fn expr_replace(expr: ExExpr, pat: String, value: String) -> ExExpr {
     let expr = expr.clone_inner();

native/explorer/src/lib.rs

@@ -271,6 +271,7 @@ rustler::init!(
         expr_lstrip,
         expr_rstrip,
         expr_substring,
+        expr_split,
         expr_replace,
         expr_json_path_match,
         // float round expressions

test/explorer/data_frame_test.exs

@@ -1733,6 +1733,17 @@ defmodule Explorer.DataFrameTest do
              }
     end
 
+    test "split a string by a substring" do
+      df = DF.new(a: ["foo,bar", "bar,baz"])
+
+      df1 = DF.mutate(df, b: split(a, ","))
+
+      assert DF.to_columns(df1, atom_keys: true) == %{
+               a: ["foo,bar", "bar,baz"],
+               b: [["foo", "bar"], ["bar", "baz"]]
+             }
+    end
+
     test "replace characters in a string" do
       df = DF.new(a: ["2,000", "2,000,000", ","])