Control the types on sklearn internal read table

We do this only for KhiopsClassifier and KhiopsRegressor: It is critical
for KhiopsClassifier as it accepts many target types and it is trivial
in the case of KhiopsRegressor.

For KhiopsEncoder and KhiopsCoclustering is less critical and for the
first one it is very complex. We left them as TODO's.

Additionaly, we now also check in the "output type" tests that the
result of predict is correct. Before we only checked only that the
classes_ attribute was ok. This is to further ensure correctness.

Author: folmos-at-orange

khiops/sklearn/dataset.py

@@ -346,7 +346,7 @@ def get_khiops_variable_name(column_id):
     return variable_name
 
 
-def read_internal_data_table(file_path_or_stream):
+def read_internal_data_table(file_path_or_stream, column_dtypes=None):
     """Reads into a DataFrame a data table file with the internal format settings
 
     The table is read with the following settings:
@@ -357,18 +357,34 @@ def read_internal_data_table(file_path_or_stream):
     - Use `csv.QUOTE_MINIMAL`
     - double quoting enabled (quotes within quotes can be escaped with '""')
     - UTF-8 encoding
+    - User-specified dtypes (optional)
 
     Parameters
     ----------
     file_path_or_stream : str or file object
         The path of the internal data table file to be read or a readable file
         object.
+    column_dtypes : dict, optional
+        Dictionary linking column names with dtypes. See ``dtype`` parameter of the
+        `pandas.read_csv` function. If not set, then the column types are detected
+        automatically by pandas.
 
     Returns
     -------
     `pandas.DataFrame`
-        The dataframe representation.
+        The dataframe representation of the data table.
     """
+    # Change the 'U' types (Unicode strings) to 'O' because pandas does not support them
+    # in read_csv
+    if column_dtypes is not None:
+        execution_column_dtypes = {}
+        for column_name, dtype in column_dtypes.items():
+            if hasattr(dtype, "kind") and dtype.kind == "U":
+                execution_column_dtypes[column_name] = np.dtype("O")
+    else:
+        execution_column_dtypes = None
+
+    # Read and return the dataframe
     return pd.read_csv(
         file_path_or_stream,
         sep="\t",
@@ -377,6 +393,7 @@ def read_internal_data_table(file_path_or_stream):
         quoting=csv.QUOTE_MINIMAL,
         doublequote=True,
         encoding="utf-8",
+        dtype=execution_column_dtypes,
     )
 
 
@@ -1132,6 +1149,11 @@ def __repr__(self):
             f"dtypes={dtypes_str}>"
         )
 
+    def get_column_dtype(self, column_id):
+        if column_id not in self.data_source.dtypes:
+            raise KeyError(f"Column '{column_id}' not found in the dtypes field")
+        return self.data_source.dtypes[column_id]
+
     def create_table_file_for_khiops(
         self, output_dir, sort=True, target_column=None, target_column_id=None
     ):
@@ -1214,6 +1236,9 @@ def __repr__(self):
             f"dtype={dtype_str}; target={self.target_column_id}>"
         )
 
+    def get_column_dtype(self, _):
+        return self.data_source.dtype
+
     def create_table_file_for_khiops(
         self, output_dir, sort=True, target_column=None, target_column_id=None
     ):
@@ -1300,6 +1325,9 @@ def __repr__(self):
             f"dtype={dtype_str}>"
         )
 
+    def get_column_dtype(self, _):
+        return self.data_source.dtype
+
     def create_khiops_dictionary(self):
         """Creates a Khiops dictionary representing this sparse table