review changes

lib/explorer/backend/lazy_series.ex

@@ -125,6 +125,7 @@ defmodule Explorer.Backend.LazySeries do
     downcase: 1,
     substring: 3,
     split: 2,
+    json_decode: 2,
     # Float round
     round: 2,
     floor: 1,
@@ -143,8 +144,7 @@ defmodule Explorer.Backend.LazySeries do
     lengths: 1,
     member: 3,
     # Struct functions
-    field: 2,
-    json_decode: 2
+    field: 2
   ]
 
   @comparison_operations [:equal, :not_equal, :greater, :greater_equal, :less, :less_equal]

lib/explorer/backend/series.ex

@@ -286,6 +286,7 @@ 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 json_decode(s, dtype()) :: s
 
   # Date / DateTime
 
@@ -305,7 +306,6 @@ defmodule Explorer.Backend.Series do
 
   # Struct
   @callback field(s, String.t()) :: s
-  @callback json_decode(s, dtype()) :: s
 
   # Functions
 

lib/explorer/polars_backend/expression.ex

@@ -135,15 +135,15 @@ defmodule Explorer.PolarsBackend.Expression do
     upcase: 1,
     substring: 3,
     split: 2,
+    json_decode: 2,
 
     # Lists
     join: 2,
     lengths: 1,
     member: 3,
 
     # Structs
-    field: 2,
-    json_decode: 2
+    field: 2
   ]
 
   @custom_expressions [

lib/explorer/series.ex

@@ -6044,7 +6044,7 @@ defmodule Explorer.Series do
   end
 
   @doc """
-  Converts a string series containing valid json to a struct series.
+  Converts a string series containing valid json to a series.
 
   ## Examples
 
@@ -6055,10 +6055,28 @@ defmodule Explorer.Series do
         struct[1] [%{"a" => 1}]
       >
 
-  Will raise `RuntimeError` for invalid json.
+      iex> s = Series.from_list(["1"])
+      iex> Series.json_decode(s, {:s, 64})
+      #Explorer.Series<
+        Polars[1]
+        s64 [1]
+      >
+
+  Will raise `RuntimeError` if the string is invalid json. 
+
+  Decoded value will be nil incase of a dtype mismatch e.g. string and integer.
+
+  ## Examples
+
+      iex> s = Series.from_list(["\\"1\\""])
+      iex> Series.json_decode(s, {:s, 64})
+      #Explorer.Series<
+        Polars[1]
+        s64 [nil]
+      >
   """
-  @doc type: :struct_wise
-  @spec json_decode(Series.t(), struct_dtype()) :: Series.t()
+  @doc type: :string_wise
+  @spec json_decode(Series.t(), dtype()) :: Series.t()
   def json_decode(%Series{dtype: :string} = series, dtype) do
     dtype = Shared.normalise_dtype!(dtype)
 

test/explorer/data_frame_test.exs

@@ -4278,4 +4278,34 @@ defmodule Explorer.DataFrameTest do
              }
     end
   end
+
+  describe "json_decode/2" do
+    test "decodes primitives, lists, structs" do
+      df = DF.new([%{st: "{\"n\": 1}", f: "1.0", l: "[1]", dt: "1"}], lazy: true)
+
+      df1 =
+        DF.mutate(df,
+          st: json_decode(st, {:struct, %{"n" => {:s, 64}}}),
+          f: json_decode(f, {:f, 64}),
+          l: json_decode(l, {:list, {:s, 64}}),
+          dt: json_decode(dt, {:datetime, :microsecond})
+        )
+
+      assert df.dtypes == %{"dt" => :string, "f" => :string, "l" => :string, "st" => :string}
+
+      assert df1.dtypes == %{
+               "dt" => {:datetime, :microsecond},
+               "f" => {:f, 64},
+               "l" => {:list, {:s, 64}},
+               "st" => {:struct, %{"n" => {:s, 64}}}
+             }
+
+      assert df1 |> DF.collect() |> DF.to_columns() == %{
+               "dt" => [~N[1970-01-01 00:00:00.000001]],
+               "f" => [1.0],
+               "l" => [[1]],
+               "st" => [%{"n" => 1}]
+             }
+    end
+  end
 end

test/explorer/series_test.exs

@@ -5868,11 +5868,19 @@ defmodule Explorer.SeriesTest do
   end
 
   describe "json_decode/2" do
-    test "extracts struct from json" do
-      s = Series.from_list(["{\"n\": 1}"])
-      sj = Series.json_decode(s, {:struct, %{"n" => {:s, 64}}})
-      assert sj.dtype == {:struct, %{"n" => {:s, 64}}}
-      assert Series.to_list(sj) == [%{"n" => 1}]
+    test "raises for invalid json" do
+      assert_raise RuntimeError,
+                   "Polars Error: error deserializing JSON: json parsing error: 'InternalError(TapeError) at character 1 ('a')'",
+                   fn ->
+                     Series.from_list(["a"]) |> Series.json_decode(:string)
+                   end
+    end
+
+    test "extracts primitive from json and nil for mismatch" do
+      s = Series.from_list(["1", "\"a\""])
+      sj = Series.json_decode(s, {:s, 64})
+      assert sj.dtype == {:s, 64}
+      assert Series.to_list(sj) == [1, nil]
     end
 
     test "extracts struct from json with dtype" do