enable adding eager series

lib/explorer/data_frame.ex

@@ -2817,15 +2817,7 @@ defmodule Explorer.DataFrame do
     Shared.apply_impl(df, :mutate_with, [df_out, column_pairs])
   end
 
-  defp value!(%Series{data: %LazySeries{}} = lazy_series) do
-    lazy_series
-  end
-
-  defp value!(%Series{data: _other}) do
-    raise ArgumentError,
-          "expecting a lazy series. Consider using `Explorer.DataFrame.put/3` " <>
-            "to add eager series to your dataframe."
-  end
+  defp value!(%Series{} = series), do: series
 
   defp value!(list) when is_list(list) do
     raise ArgumentError,

test/explorer/data_frame_test.exs

@@ -727,6 +727,20 @@ defmodule Explorer.DataFrameTest do
              }
     end
 
+    test "add series to dataframe" do
+      df = DF.new([%{a: 1}, %{a: 2}, %{a: 3}])
+      s = Explorer.Series.from_list(["x", "y", "z"])
+
+      df1 = DF.mutate(df, s: ^s, a1: a + 1)
+      assert df1.names == ["a", "s", "a1"]
+
+      assert df1.dtypes == %{
+               "a" => {:s, 64},
+               "s" => :string,
+               "a1" => {:s, 64}
+             }
+    end
+
     test "adds new columns" do
       df = DF.new(a: [1, 2, 3], b: ["a", "b", "c"])
 
@@ -1578,12 +1592,12 @@ defmodule Explorer.DataFrameTest do
              }
     end
 
-    test "raises when adding eager series" do
+    test "raises when adding eager series whose length does not match dataframe's length" do
       df = DF.new(a: [1, 2, 3])
-      series = Series.from_list([4, 5, 6])
+      series = Series.from_list([4, 5, 6, 7])
 
-      assert_raise ArgumentError,
-                   "expecting a lazy series. Consider using `Explorer.DataFrame.put/3` to add eager series to your dataframe.",
+      assert_raise RuntimeError,
+                   "Polars Error: lengths don't match: unable to add a column of length 4 to a DataFrame of height 3",
                    fn ->
                      DF.mutate(df, b: ^series)
                    end