Drop columns by name and not by index.

cml/domain/data_source.py

@@ -37,8 +37,9 @@ class DataSource:
 
 
 class Preprocessor:
-    TARGET_COLUMN = "Z"
     TIME_COLUMN = "T"
+    TARGET_COLUMN = "Z"
+    SIGMA_COLUMN = "Sigma"
 
     def __init__(self, settings):
         self.settings = settings
@@ -55,12 +56,13 @@ class Preprocessor:
         if self.settings.cut_time_stamp:
             self._remove_common_time_stamp_prefix(table)
 
+        return table
+
     def _drop_irrelevant_columns(self, table):
-        # TODO (dmt): Don't drop T, Z and Sigma columns!
-        for column in table.get_columns():
-            column_index = table.get_column_index_by_name(column)
-            if column_index not in self.settings.set_features:
-                table.drop_column_by_index(column_index)
+        features_to_be_removed = [table.get_column_name_by_index(i)
+                                  for i in self.settings.set_features]
+        for column in features_to_be_removed:
+            table.drop_column_by_name(column)
 
     def _overwrite_target_column(self, table):
         table.set_column_value(self.TARGET_COLUMN, self.settings.set_targets)