Allow deleting obs/var cols

Fixes #29

anndata/base.py

@@ -13,6 +13,7 @@
 import numpy as np
 from numpy import ma
 import pandas as pd
+from numpy.lib.recfunctions import rec_drop_fields
 from pandas.core.index import RangeIndex
 from pandas.api.types import is_string_dtype, is_categorical
 from scipy import sparse
@@ -156,6 +157,17 @@ def __setitem__(self, key, arr):
         new = BoundRecArr(new, self._parent, self._attr)
         setattr(self._parent, self._attr, new)
 
+    def __delitem__(self, key):
+        """Delete field with name."""
+        if key not in self.dtype.names:
+            raise ValueError(
+                'Currently, can only delete single names from {}.'
+                .format(self.dtype.names)
+            )
+        new_array = rec_drop_fields(self, key)
+        new = BoundRecArr(new_array, self._parent, self._attr)
+        setattr(self._parent, self._attr, new)
+
     def to_df(self):
         """Convert to pandas dataframe."""
         df = pd.DataFrame(index=RangeIndex(0, self.shape[0], name=None))

anndata/tests/base.py

@@ -187,6 +187,15 @@ def test_append_col():
         adata.obs['new4'] = 'far too long'.split()
 
 
+def test_delete_col():
+    adata = AnnData(np.array([[1, 2, 3], [4, 5, 6]]), dict(o1=[1, 2], o2=[3, 4]))
+    assert ['o1', 'o2'] == adata.obs_keys()
+
+    del adata.obs['o1']
+    assert ['o2'] == adata.obs_keys()
+    assert [3, 4] == adata.obs['o2'].tolist()
+
+
 def test_set_obs():
     adata = AnnData(np.array([[1, 2, 3], [4, 5, 6]]))