Allow filtering by a feature list.

Feature list may be created by RFE, for example

delta/__init__.py

@@ -15,7 +15,8 @@
 from .deltas import registry, Normalization, DeltaFunction, \
         PDistDeltaFunction, CompositeDeltaFunction
 from .cluster import Clustering
+from .features import get_rfe_features
 
 __all__ = [ Corpus, FeatureGenerator, LETTERS_PATTERN, WORD_PATTERN,
            registry, Normalization,
-           DeltaFunction, PDistDeltaFunction, CompositeDeltaFunction, Clustering ]
+           DeltaFunction, PDistDeltaFunction, CompositeDeltaFunction, Clustering, get_rfe_features ]

delta/corpus.py

@@ -321,6 +321,7 @@ def __init__(self, subdir=None, file=None, corpus=None,
         self.logger = logger
         self.metadata = metadata
         self.document_describer = document_describer
+        self.feature_generator = feature_generator
 
 
     def new_data(self, data, **metadata):
@@ -469,10 +470,19 @@ def filter_wordlist(self, filename, **kwargs):
             New corpus with seelected features.
         """
         words = list(self._load_wordlist(filename, **kwargs))
-        return self.new_data(
-            corpus=self.loc[:, words],
-            complete=False,
-            wordlist=filename)
+        return self.filter_features(words, wordlist=filename)
+
+    def filter_features(self, features, **metadata):
+        """
+        Returns a new corpus that contains only the given features.
+
+        Args:
+            features (Iterable):
+                The features to select. If its in a file, use filter_wordlist
+        """
+        return self.new_data(self.loc[:, features],
+                             complete=False,
+                             **metadata)
 
 
     def relative_frequencies(self):