Adapt pow/2 to follow the same rules from Polars

If exponent is float, it follows dtype of exponent. Otherwise, it follows dtype of base.
See: pola-rs/polars#15506

lib/explorer/series.ex

@@ -3595,9 +3595,13 @@ defmodule Explorer.Series do
   Raises a numeric series to the power of the exponent.
 
   At least one of the arguments must be a series. If both
-  sizes are series, the series must have the same size or
+  sides are series, the series must have the same size or
   at last one of them must have size of 1.
 
+  Note that this operation can fail if the exponent is a
+  signed integer series or scalar containing negative values,
+  and the base is also of an integer type.
+
   ## Supported dtypes
 
     * floats: #{Shared.inspect_dtypes(@float_dtypes, backsticks: true)}

test/explorer/series_test.exs

@@ -2283,7 +2283,7 @@ defmodule Explorer.SeriesTest do
       end
     end
 
-    test "pow(uint, sint) == float64" do
+    test "pow(uint, sint) == sint" do
       for u_base <- [8, 16, 32, 64], s_power <- [8, 16, 32, 64] do
         base = Series.from_list([1, 2, 3], dtype: {:u, u_base})
         power = Series.from_list([3, 2, 1], dtype: {:s, s_power})
@@ -2308,7 +2308,7 @@ defmodule Explorer.SeriesTest do
       end
     end
 
-    test "pow(sint, sint) == float64" do
+    test "pow(sint, sint) == sint" do
       for s_base <- [8, 16, 32, 64], s_power <- [8, 16, 32, 64] do
         base = Series.from_list([1, 2, 3], dtype: {:s, s_base})
         power = Series.from_list([3, 2, 1], dtype: {:s, s_power})
@@ -2360,10 +2360,13 @@ defmodule Explorer.SeriesTest do
       s1 = Series.from_list([1, 2, 3])
       s2 = Series.from_list([1, -2, 3])
 
-      result = Series.pow(s1, s2)
+      message =
+        "Polars Error: invalid operation: invalid operation: conversion from `i64` to `u32` failed in column 'exponent' for 1 out of 3 values: [-2]\n\n" <>
+          "Hint: if you were trying to raise an integer to a negative integer power, please cast your base or exponent to float first."
 
-      assert result.dtype == {:f, 64}
-      assert Series.to_list(result) === [1.0, 0.25, 27.0]
+      assert_raise RuntimeError, message, fn ->
+        Series.pow(s1, s2)
+      end
     end
 
     test "pow of an integer series with a float series" do
@@ -2428,10 +2431,13 @@ defmodule Explorer.SeriesTest do
     test "pow of an integer series with a negative integer scalar value on the right-hand side" do
       s1 = Series.from_list([1, 2, 3])
 
-      result = Series.pow(s1, -2)
+      message =
+        "Polars Error: invalid operation: invalid operation: conversion from `i64` to `u32` failed in column 'literal' for 1 out of 1 values: [-2]\n\n" <>
+          "Hint: if you were trying to raise an integer to a negative integer power, please cast your base or exponent to float first."
 
-      assert result.dtype == {:f, 64}
-      assert Series.to_list(result) === [1.0, 1 / 4, 1 / 9]
+      assert_raise RuntimeError, message, fn ->
+        Series.pow(s1, -2)
+      end
     end
 
     test "pow of an integer series with a float scalar value on the right-hand side" do
@@ -2484,25 +2490,28 @@ defmodule Explorer.SeriesTest do
 
       result = Series.pow(2, s1)
 
-      assert result.dtype == {:f, 64}
-      assert Series.to_list(result) === [2.0, 4.0, 8.0]
+      assert result.dtype == {:s, 64}
+      assert Series.to_list(result) === [2, 4, 8]
     end
 
     test "pow of an integer series that contains negative integer with an integer scalar value on the left-hand side" do
       s1 = Series.from_list([1, -2, 3])
 
-      result = Series.pow(2, s1)
+      message =
+        "Polars Error: invalid operation: invalid operation: conversion from `i64` to `u32` failed in column 'exponent' for 1 out of 3 values: [-2]\n\n" <>
+          "Hint: if you were trying to raise an integer to a negative integer power, please cast your base or exponent to float first."
 
-      assert result.dtype == {:f, 64}
-      assert Series.to_list(result) === [2.0, 0.25, 8.0]
+      assert_raise RuntimeError, message, fn ->
+        Series.pow(2, s1)
+      end
     end
 
     test "pow of an integer series with a negative integer scalar value on the left-hand side" do
       s1 = Series.from_list([1, 2, 3])
 
       result = Series.pow(-2, s1)
 
-      assert result.dtype == {:f, 64}
+      assert result.dtype == {:s, 64}
       assert Series.to_list(result) == [-2, 4, -8]
     end